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Magnets and electric charges show certain similarities. For example, both magnets and electric charges can exert a force on their surroundings. This force, when produced by a magnet, is called a magnetic field. When it is produced by an electric charge, the force is called an electric field. It has been observed that the strength of both magnetic fields and electric fields is inversely proportional to the square of the distance between a magnet or an electric charge and the objects that they affect.
Below, three scientists debate the relationship between electricity and magnetism.
Scientist 1:
Electricity and magnetism are two different phenomena. Materials such as iron, cobalt, and nickel contain magnetic domains: tiny regions of magnetism, each with two poles. Normally, the domains have a random orientation and are not aligned, so the magnetism of some domains cancels out that of other domains; however, in magnets, domains line up in the same direction, creating the two poles of the magnet and causing magnetic behavior.
In contrast, electricity is a moving electric charge which is caused by the flow of electrons through a material. Electrons flow through a material from a region of higher potential (more negative charge) to a region of lower potential (more positive charge). We can measure this flow of electrons as current, which refers to the amount of charge transferred over a period of time.
Scientist 2:
Electricity and magnetism are similar phenomena; however, one cannot be reduced to the other. Electricity involves two types of charges: positive and negative charge. Though electricity can occur in a moving form (in the form of current, or an electric charge moving through a wire), it can also occur in a static form. Static electricity involves no moving charge. Instead, objects can have a net excess of positive charge or a net excess of negative charge—because of having lost or gained electrons, respectively. When two static positive electric charges or two static negative electric charges are brought close together, they repel each other. However, when a positive and a negative static charge are brought together, they attract each other.
Similarly, all magnets have two poles. Magnetic poles that are alike repel each other, while dissimilar magnetic poles attract each other. Magnets and static electric charges are alike in that they both show attraction and repulsion in similar circumstances. However, while isolated static electric charges occur in nature, there are no single, isolated magnetic poles. All magnets have two poles, which cannot be dissociated from each other.
Scientist 3:
Electricity and magnetism are two aspects of the same phenomenon. A moving flow of electrons creates a magnetic field around it. Thus, wherever an electric current exists, a magnetic field will also exist. The magnetic field created by an electric current is perpendicular to the electric current's direction of flow.
Additionally, a magnetic field can induce an electric current. This can happen when a wire is moved across a magnetic field, or when a magnetic field is moved near a conductive wire. Because magnetic fields can produce electric fields and electric fields can produce magnetic fields, we can understand electricity and magnetism as parts of one phenomenon: electromagnetism.
In an experiment, an iron bar that showed no magnetism was heated and allowed to cool while aligned North-South with the Earth's magnetic field. After it cooled, the iron bar was found to be magnetic. Scientist 1 would most likely explain this result by saying which of the following?
The experiment allowed the magnetic domains of the bar to line up, causing the bar to become magnetic.
The experiment induced an electric current in the bar, causing the bar to become magnetic.
The experiment caused the magnetic domains of the bar to move out of alignment with each other.
The experiment caused the two magnetic poles of the bar to move so that they were aligned with the Earth's magnetic field.
Interference occurred between the electric field of the bar and the magnetic field of the Earth, causing the bar to become magnetic.
Scientist 1 states that magnetism occurs when the magnetic domains in a material align. Since the iron bar initially showed no magnetism, we can assume that its magnetic domains were initially oriented randomly, and that it had no magnetic poles. Since the iron bar became magnetic after it was heated and cooled, the heating and cooling process likely reoriented the magnetic domains in the iron so that they became more aligned, creating two magnetic poles.
A company developed new prototype car and wanted to test the new car. The car's acceleration time from 0mph to 60mph and stopping time from 60mph to 0mph were measured. An obstacle course involving a lot of turns was also constructed to determine how well the car can handle turning. The main concern of the company is the safety of the car and therefore all of the tests were performed on dry concrete, concrete after simulated rain, concrete that was covered with snow and in sand.
In order for the car to be safe on the roads, it is necessary for the car to have a stopping time of 4.5 seconds. What surfaces would the car not be safe on?
Rain and snow
All surfaces
Sand, snow and rain
Sand and rain
The necessary stopping time is 4.5 seconds. When it comes to stopping time, the shorter the time the better for avoiding any hazards. Therefore the stopping times that are longer than 4.5 seconds are not safe. The rainy condition has a stopping time of 5.0 seconds and the snowy condition has a stopping time of 6.2 seconds. These two conditions are not safe when using this car.
A group of scientists wanted to test the effects of Nitra-Grow, a chemical additive that can be given to plants to help them grow. 3 test groups of plants were given all the same time of sunlight, the same type of soil, and the same amount of water. Plant A was given no extra chemicals. Plant B was given 5g of Nitra-Grow. Plant C was given 5g of Ammonia to see if Nitra-Grow worked any better than a basic nitrogen-based household product. The plants are then measured on 5 consecutive days to find their average height (in cm).
DAY | Height Plant A (cm) | Height Plant B (cm) | Height Plant C (cm) |
---|---|---|---|
1 | 1.2 | 1.2 | 1.2 |
2 | 1.4 | 1.4 | 1.2 |
3 | 1.6 | 1.8 | 1.3 |
4 | 1.8 | 2.4 | 1.3 |
5 | 2.0 | 2.6 | 1.4 |
What is the general relationship between plant height and the amount of days?
As time increases, the plant height increases.
As time increases, the plant height increases, then decreases.
As the plant height increases, the time increases.
As the plant height increases, the time decreases.
There is no relationship between time and height of the plants.
As time increases, the heights of all plants increase (except for plant B on day 6). The day doesn't change just because the plants grow.
Scientist 1: This scientist claims that the current in a circuit flows from the positive side of a battery to the negative side of the battery. In other words, the protons in the circuit are responsible for the flow of electricity.
Scientist 2: This scientist asserts that the current in a circuit flows from the negative side of a battery to the positive side of the battery. In other words, the electrons in the circuit are responsible for the flow of electricity.
Experiment A: The scientists construct a circuit that contains just a battery, a switch and light bulb. The wiring is made of copper. The scientists turn the switch from off to on. It is noticed that the light bulb turns on.
Experiment B: The scientists have developed a novel metal that allows for only electrons to travel through the metal, but does not allow protons to travel through the metal. The scientists construct the same circuit as in Experiment A, using this material as the wiring. When the switch is turned on, the light bulb turns on.
Experiment C: The scientists have also constructed a metal that allows for only protons to travel through the metal, but does not allow for electrons to travel through the metal. The same circuit as in Experiment A is constructed, but with the wiring being made by this innovative metal. When the switch is turned on, the light bulb does not turn on.
Whose viewpoints are supported or disproved by Experiment C?
Scientist 1's viewpoint is disproved; Scientist 2's viewpoint is neither supported nor disproved
Scientist 1's viewpoint is neither proved or disproved; Scientist 2's viewpoint is disproved
Scientist 1's viewpoint is disproved; Scientist 2's viewpoint is disproved
Scientist 1's viewpoint is supported; Scientist 2's viewpoint is supported
The circuit allows for the flow of protons and it is noticed that the light bulb does not turn on. Therefore the protons in the circuit are not responsible for the flow of electricity as the light bulb would turn on if there was a flow of electricity. Scientist 1's viewpoint is disproven. There is nothing said about the flow of electrons in this experiment and therefore Scientist 2's viewpoint is neither proven nor disproven.
Magnets and electric charges show certain similarities. For example, both magnets and electric charges can exert a force on their surroundings. This force, when produced by a magnet, is called a magnetic field. When it is produced by an electric charge, the force is called an electric field. It has been observed that the strength of both magnetic fields and electric fields is inversely proportional to the square of the distance between a magnet or an electric charge and the objects that they affect.
Below, three scientists debate the relationship between electricity and magnetism.
Scientist 1:
Electricity and magnetism are two different phenomena. Materials such as iron, cobalt, and nickel contain magnetic domains: tiny regions of magnetism, each with two poles. Normally, the domains have a random orientation and are not aligned, so the magnetism of some domains cancels out that of other domains; however, in magnets, domains line up in the same direction, creating the two poles of the magnet and causing magnetic behavior.
In contrast, electricity is a moving electric charge which is caused by the flow of electrons through a material. Electrons flow through a material from a region of higher potential (more negative charge) to a region of lower potential (more positive charge). We can measure this flow of electrons as current, which refers to the amount of charge transferred over a period of time.
Scientist 2:
Electricity and magnetism are similar phenomena; however, one cannot be reduced to the other. Electricity involves two types of charges: positive and negative charge. Though electricity can occur in a moving form (in the form of current, or an electric charge moving through a wire), it can also occur in a static form. Static electricity involves no moving charge. Instead, objects can have a net excess of positive charge or a net excess of negative charge—because of having lost or gained electrons, respectively. When two static positive electric charges or two static negative electric charges are brought close together, they repel each other. However, when a positive and a negative static charge are brought together, they attract each other.
Similarly, all magnets have two poles. Magnetic poles that are alike repel each other, while dissimilar magnetic poles attract each other. Magnets and static electric charges are alike in that they both show attraction and repulsion in similar circumstances. However, while isolated static electric charges occur in nature, there are no single, isolated magnetic poles. All magnets have two poles, which cannot be dissociated from each other.
Scientist 3:
Electricity and magnetism are two aspects of the same phenomenon. A moving flow of electrons creates a magnetic field around it. Thus, wherever an electric current exists, a magnetic field will also exist. The magnetic field created by an electric current is perpendicular to the electric current's direction of flow.
Additionally, a magnetic field can induce an electric current. This can happen when a wire is moved across a magnetic field, or when a magnetic field is moved near a conductive wire. Because magnetic fields can produce electric fields and electric fields can produce magnetic fields, we can understand electricity and magnetism as parts of one phenomenon: electromagnetism.
According to Scientist 2, which of the following would be an example of a static electric charge?
A balloon that has been rubbed against hair so that it has picked up excess electrons
A wire that carries charge from the negative to the positive terminal of a battery
A bar magnet placed in an electric field
A ring of a conductive material, such copper, that has not lost or gained electrons
A conductive material, such as copper, that is placed in an magnetic field
Scientist 2 states that static electric charges occur when an object has a net excess of positive or negative charge. According to Scientist 2, static electric charges also don't involve a moving charge. So, one example of a static electric charge is a balloon that has picked up excess electrons: it has an excess of negative charge, but the charge is not moving.
Sleep plays a vital role in defining the daily activities of virtually all animals. During periods of sleep, the parasympathetic nervous system becomes active and induces a relaxed state in response to increased levels of the hormone melatonin. Yet, despite its ubiquity in the animal kingdom, the purpose of sleep and its role in our daily lives has been disputed by scientists. Two scientists discuss their theories about the purpose of sleep.
Scientist 1
During periods of sleep, animals are able to conserve energy that they would otherwise be spending on unnecessary activity. If an animal’s primary food source is most abundant during daylight, it is a waste of precious energy to be moving about at night. For example, many herbivores, such as squirrels, are diurnal (sleep during the night) because their food source is available during the day, while many insectivores, such as bats, are nocturnal (sleep during the day) because their food source is available during the night. Food sources, as an animal’s most valuable resource, dictate their sleep cycles. Many animal traits observable today evolved as a result of the supply and demand of food in their natural habitat.
Scientist 2
During waking hours, it is true that the body utilizes large amounts of energy. However, the role of sleep is to restore biological products that were utilized during periods of wakefulness, rather than simply avoid utilizing energy in the first place. Many types of biological molecules, such as hormones, are released throughout the body while an animal is active. Sleep serves as a period of inactivity during which the body can manufacture and store a supply of these molecules for future use during the next period of activity. Furthermore, sleep allows the body to repair cellular damages that has accumulated during waking hours. Experimental evidence shows that when animals are deprived of sleep, their immune system quickly weakens and death rates increase. Sleep is necessary for animals to prevent accumulation of damage and to regenerate crucial biomolecules for daily life.
Both scientists give evidence to support their theories. The evidence given by Scientist 1 can best be described as __________.
observational
quantitative
empirical
experimental
natural
Scientist 1 gives two examples of animals that appear to follow the trends of his theory. "For example, many herbivores, such as squirrels, are diurnal . . . while many insectivores, such as bats, are nocturnal"
This evidence is strictly observational. There is no experimental set-up, quantitative or empirical data. Though the evidence is observation of animals in their natural state, observational is a commonly used classification of evidence, while natural is not, making observational the best answer choice.
Magnets and electric charges show certain similarities. For example, both magnets and electric charges can exert a force on their surroundings. This force, when produced by a magnet, is called a magnetic field. When it is produced by an electric charge, the force is called an electric field. It has been observed that the strength of both magnetic fields and electric fields is inversely proportional to the square of the distance between a magnet or an electric charge and the objects that they affect.
Below, three scientists debate the relationship between electricity and magnetism.
Scientist 1:
Electricity and magnetism are two different phenomena. Materials such as iron, cobalt, and nickel contain magnetic domains: tiny regions of magnetism, each with two poles. Normally, the domains have a random orientation and are not aligned, so the magnetism of some domains cancels out that of other domains; however, in magnets, domains line up in the same direction, creating the two poles of the magnet and causing magnetic behavior.
In contrast, electricity is a moving electric charge which is caused by the flow of electrons through a material. Electrons flow through a material from a region of higher potential (more negative charge) to a region of lower potential (more positive charge). We can measure this flow of electrons as current, which refers to the amount of charge transferred over a period of time.
Scientist 2:
Electricity and magnetism are similar phenomena; however, one cannot be reduced to the other. Electricity involves two types of charges: positive and negative charge. Though electricity can occur in a moving form (in the form of current, or an electric charge moving through a wire), it can also occur in a static form. Static electricity involves no moving charge. Instead, objects can have a net excess of positive charge or a net excess of negative charge—because of having lost or gained electrons, respectively. When two static positive electric charges or two static negative electric charges are brought close together, they repel each other. However, when a positive and a negative static charge are brought together, they attract each other.
Similarly, all magnets have two poles. Magnetic poles that are alike repel each other, while dissimilar magnetic poles attract each other. Magnets and static electric charges are alike in that they both show attraction and repulsion in similar circumstances. However, while isolated static electric charges occur in nature, there are no single, isolated magnetic poles. All magnets have two poles, which cannot be dissociated from each other.
Scientist 3:
Electricity and magnetism are two aspects of the same phenomenon. A moving flow of electrons creates a magnetic field around it. Thus, wherever an electric current exists, a magnetic field will also exist. The magnetic field created by an electric current is perpendicular to the electric current's direction of flow.
Additionally, a magnetic field can induce an electric current. This can happen when a wire is moved across a magnetic field, or when a magnetic field is moved near a conductive wire. Because magnetic fields can produce electric fields and electric fields can produce magnetic fields, we can understand electricity and magnetism as parts of one phenomenon: electromagnetism.
In an experiment, an iron bar that showed no magnetism was heated and allowed to cool while aligned North-South with the Earth's magnetic field. After it cooled, the iron bar was found to be magnetic. Scientist 1 would most likely explain this result by saying which of the following?
The experiment allowed the magnetic domains of the bar to line up, causing the bar to become magnetic.
The experiment induced an electric current in the bar, causing the bar to become magnetic.
The experiment caused the magnetic domains of the bar to move out of alignment with each other.
The experiment caused the two magnetic poles of the bar to move so that they were aligned with the Earth's magnetic field.
Interference occurred between the electric field of the bar and the magnetic field of the Earth, causing the bar to become magnetic.
Scientist 1 states that magnetism occurs when the magnetic domains in a material align. Since the iron bar initially showed no magnetism, we can assume that its magnetic domains were initially oriented randomly, and that it had no magnetic poles. Since the iron bar became magnetic after it was heated and cooled, the heating and cooling process likely reoriented the magnetic domains in the iron so that they became more aligned, creating two magnetic poles.
In a physics class, students conducted a series of experiments by placing different objects into a beaker of water. They conducted twenty trials for each object. For each trial, they recorded whether or not the object floated.
First, they placed a steel paper clip into the water. They observed that the paper clip usually sank; however, they also saw that occasionally, the paper clip stayed afloat if it was placed very gently on top of the water. Next, they repeated the the same procedure using a cork, a toy boat made of aluminum, and a glass marble. They observed that both the cork and the toy boat always stayed afloat in the water, but that the glass marble always sank.
Below, three students give their explanations for these observations.
Student 1:
Objects float when they are less dense than the liquid in which they are immersed. For example, when immiscible liquids of varying densities are mixed together in a container, the most dense liquid will sink to the bottom of the container, while the least dense liquid will rise to the top. This same principle applies to solid objects. Because the cork and the aluminum toy boat always float, cork and the aluminum of the boat must be less dense than water. Because the glass marble always sinks, the glass of the marble must be more dense than water.
Objects that are more dense than water can also float due to surface tension. Surface tension occurs because molecules of a liquid are more attracted to each other more than they are to other objects. Molecules on the surface of water are attracted to the molecules around them and below them. This attraction causes a liquid's surface to behave if it were covered by a thin film, which resists penetration by other objects. Therefore, small objects such as paper clips can sometimes float on water when the upward force of water's surface tension exceeds the force of gravity pulling such objects down. Because the paper clips often sink and only float sometimes, we can conclude that they are indeed more dense than water, and that their floating is due to surface tension.
Student 2:
Objects float in two different cases: when they are buoyed by a liquid's surface tension or when their average density is less than that of the liquid in which they are immersed. The average density of cork is less than that of water. This is why the cork floats. In contrast, the density of glass is more than that of water. This is why the glass marble sinks.
However, the densities of aluminum and of steel are greater than that of water. Thus, density cannot be used to explain why the aluminum toy boat and the paper clip float. Both of these objects float because of surface tension. Because the paper clip does not have much mass, the normal upward force created by water's surface tension can be enough to allow it to float. Other objects with greater mass, like the toy boat, employ a particular shape to magnify the force of surface tension. The curved shape of the boat's bottom both stabilizes the boat and increases the amount of the boat's surface area that touches the water, maximizing the force due to surface tension that the boat receives.
Student 3:
In this experiment, the paper clip floats because of surface tension; however, the cork, toy boat, and marble float or sink because of their relationship to a buoyant force. All objects immersed in a liquid experience a buoyant force, which pushes them upward. The strength of this force is equal to the weight of the liquid displaced, or pushed aside, by an object. Every object also experiences a downward force due to gravity, which is measured as the object's weight, and which is directly proportional to the object's mass. When the buoyant force acting on an object is greater than the downward force due to gravity, the object floats. However, when the buoyant force is less than the force due to gravity, the object sinks. Both the cork and the aluminum toy boat are able to displace enough water to create a buoyant force that exceeds the force due to gravity, so they float. However, the glass marble does not displace enough water to create a sufficient buoyant force, so it sinks.
Paint is more dense than cooking oil; however, when a drop of paint is dripped into a container of cooking oil, it floats on top of the oil. If Student 1's explanation is correct, which of the following is most likely the reason for this observation?
The force on the drop of paint due to surface tension is greater than the force due to gravity.
The force on the drop of paint due to surface tension is less than the force due to gravity.
The buoyant force on the drop of paint is greater than the force due to gravity.
The buoyant force on the drop of paint is less than the force due to gravity.
The force on the drop of paint due to surface tension is less than the buoyant force.
Student 1 says that objects may either float because they are less dense than water or because they rest on top of water due to the water's surface tension. Since we know that the drop of paint is more dense than water, it must float because of surface tension. According to Student 1, when something floats due to surface tension, the upward force from surface tension exceeds the downward force that gravity exerts on the drop of paint.
Magnets and electric charges show certain similarities. For example, both magnets and electric charges can exert a force on their surroundings. This force, when produced by a magnet, is called a magnetic field. When it is produced by an electric charge, the force is called an electric field. It has been observed that the strength of both magnetic fields and electric fields is inversely proportional to the square of the distance between a magnet or an electric charge and the objects that they affect.
Below, three scientists debate the relationship between electricity and magnetism.
Scientist 1:
Electricity and magnetism are two different phenomena. Materials such as iron, cobalt, and nickel contain magnetic domains: tiny regions of magnetism, each with two poles. Normally, the domains have a random orientation and are not aligned, so the magnetism of some domains cancels out that of other domains; however, in magnets, domains line up in the same direction, creating the two poles of the magnet and causing magnetic behavior.
In contrast, electricity is a moving electric charge which is caused by the flow of electrons through a material. Electrons flow through a material from a region of higher potential (more negative charge) to a region of lower potential (more positive charge). We can measure this flow of electrons as current, which refers to the amount of charge transferred over a period of time.
Scientist 2:
Electricity and magnetism are similar phenomena; however, one cannot be reduced to the other. Electricity involves two types of charges: positive and negative charge. Though electricity can occur in a moving form (in the form of current, or an electric charge moving through a wire), it can also occur in a static form. Static electricity involves no moving charge. Instead, objects can have a net excess of positive charge or a net excess of negative charge—because of having lost or gained electrons, respectively. When two static positive electric charges or two static negative electric charges are brought close together, they repel each other. However, when a positive and a negative static charge are brought together, they attract each other.
Similarly, all magnets have two poles. Magnetic poles that are alike repel each other, while dissimilar magnetic poles attract each other. Magnets and static electric charges are alike in that they both show attraction and repulsion in similar circumstances. However, while isolated static electric charges occur in nature, there are no single, isolated magnetic poles. All magnets have two poles, which cannot be dissociated from each other.
Scientist 3:
Electricity and magnetism are two aspects of the same phenomenon. A moving flow of electrons creates a magnetic field around it. Thus, wherever an electric current exists, a magnetic field will also exist. The magnetic field created by an electric current is perpendicular to the electric current's direction of flow.
Additionally, a magnetic field can induce an electric current. This can happen when a wire is moved across a magnetic field, or when a magnetic field is moved near a conductive wire. Because magnetic fields can produce electric fields and electric fields can produce magnetic fields, we can understand electricity and magnetism as parts of one phenomenon: electromagnetism.
Which of the following would be an example of electricity according to Scientist 2, but not according to Scientist 1?
Two negatively-charged objects repel each other.
A positively-charged object is attracted to a negatively-charged object and receives excess electrons from it.
A wire conducts electrons from the negative terminal of a battery to the positive terminal.
Current flows along a wire between a negatively-charged object and an positively charged-object.
According to Scientist 2, electricity can take on two forms: static electricity and current electricity. Scientist 2 states that while current electricity consists of a moving electric charge, static electricity involves no moving charge. Scientist 2 also states that static electricity can cause two objects to repel or attract each other. In contrast, Scientist 1 defines electricity as a moving charge—he states that electricity must involve the flow of electrons.
So, a situation where there is no flow of electrons—where two objects repel each other due to static electricity—would be seen as an example of electricity by Scientist 2, but not by Scientist 1.
As part of an engineering competition, a group of students are asked to design a flying robot that simulates the way real birds fly. Below, three of the students give their explanations for how bird flight occurs.
Student 1:
Birds are able to fly due to the shape of their wings. Bird wings are convex on their upper sides, while their lower sides are usually concave. This type of shape is called an airfoil. When a wing travels through the air, air passing over the top of the wing must travel a greater distance than air passing under the wing. The stream of air passing over the wing and the stream of air passing under the wing meet together at the tail end of the wing. In order for both streams of air to meet at the same point behind the wing, the air above the wing, which travels a greater distance, must travel faster than the air below the wing.
When a volume of air travels more quickly over a distance, its molecules are spread out over a greater distance. As a result, the air traveling over the top of a wing has a lower pressure than the air traveling under the wing. Because the wing has a region of low pressure above it and a region of relative high pressure below it, it experiences a net upward force. When this upward force is greater than or equal to the bird's weight, or the force exerted on a bird by gravity, the bird is able to fly.
The magnitude of the upward force depends on the speed at which air flows across the wing and on the corresponding difference in pressure over and under the wing. When birds flap their wings, they increase the speed of air flowing across their wings, thus producing a greater upward force.
Student 2:
There are two components to bird flight: lift and thrust. "Lift" refers to the upward force that allows a bird to stay aloft in the air despite its weight, while "thrust" refers to the horizontal force that allows a bird to move forward through the air. Birds are able to fly because they do not hold their wings perfectly horizontally. Instead, their wings are angled slightly upward. The angle at which a wing is inclined upward, with respect to the horizontal, is called its "angle of attack."
Air is not an ideal gas; instead, it has viscosity. This means that the air flowing close to a solid object tends to follow the curves of that object. When air encounters a bird's wing, it follows the incline of the wing. Because of the wing's angle of attack, the air is directed downward and back. The air continues to move downward, even after it has left the wing. This movement of the air creates an opposing force that pushes the bird upward and forward.
Thus, the angle of attack of a bird's wings accounts for both the lift and thrust components of a bird's flight.
Student 3:
Birds are able to fly because the way in which they move their wings allows them to create a net movement of air downward and backward. The flapping of a bird's wings can be understood as being composed of two parts: a downstroke, during which the bird moves its wings down, and an upstroke, during which the bird moves its wings up. During a downstroke, a bird displaces a quantity of air downward and behind it. During an upstroke, however, the bird's wings are angled upward in a way that displaces less air, and its wing feathers rotate to allow air to pass through them. Thus, on the upstroke, the bird much exerts less force on the air than it does on the downstroke.
Suppose that, in designing a hovercraft, engineers position a fan so that it blows out air straight down from the bottom of the hovercraft. Given that Student 2's explanation is correct, this would generate which of the following?
Lift
Thrust
Both lift and thrust
Neither lift nor thrust
Student 2 states that the movement of air creates and equal and opposing force which pushes a bird (or any other flying object) in the opposite direction. So, if the fan on the hovercraft blows air downward, this would generate an upward force which acts on the hovercraft. Student 2 states that the upward force experienced by a flying object is called lift.