Unit 3: Gravity Study Guide
Gravitational Force, Attraction, and Mass
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Gravitational Force: The attractive force between two objects with mass. This force depends on the masses of the objects and the distance between them.
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Weight: The force exerted by gravity on an object, calculated by the equation \( \text{Weight} = \text{mass} \times \text{acceleration due to gravity} \) (W = mg).
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Mass: The amount of matter in an object, which does not change regardless of location. Mass is measured in kilograms (kg).
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Gravitational Attraction: The pull that a massive object exerts on another object due to its mass.
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How are mass and weight different? Mass is a measure of the amount of substance in an object and is constant, while weight is the gravitational force acting on that mass, which can vary with location (e.g., from Earth to Mars).
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Would the force of gravity be the same or different on a compact car and a large tractor trailer? The force of gravity depends on the mass of the objects. Therefore, the gravitational force would be different due to the different masses of the two vehicles.
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Would a person’s weight be the same or different on Mars as it is on Earth? What about his/her mass? A person's weight would be different on Mars due to the lower gravitational force, but their mass would remain the same.
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Which object would feel heavier on Earth: a single apple or a bag of apples? A bag of apples would feel heavier because it has a greater mass.
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Why is gravitational attraction less on the moon than it is on Earth? Gravitational attraction is less on the Moon because it has a smaller mass and a smaller radius compared to Earth, leading to a weaker gravitational pull.
Investigating Gravity
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Acceleration: The rate of change of velocity of an object, measured in meters per second squared (m/s²).
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Gravity: The force that attracts two bodies toward each other, particularly the attraction of the Earth for objects near its surface.
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You drop balls of varying mass (foam ball, soccer ball, bowling ball) from the same height on Earth. Will they reach the Earth at the same time? Yes, they will reach the Earth at the same time in the absence of air resistance.
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What does this tell us about the force of gravity on objects with different masses? It indicates that the acceleration due to gravity is the same for all objects regardless of their mass.
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The acceleration due to gravity is the (same/different) for objects with different masses. (same)
Analyzing Gravitational Data
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Air resistance: The force that opposes the motion of an object as it moves through air.
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Air resistance acts opposite of what force? Air resistance acts opposite to the direction of gravity.
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If you drop a feather and a bowling ball from the same height, would they reach the ground at the same time (assuming there is no air resistance)? Yes, they would reach the ground at the same time without air resistance.
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Why do a feather and a bowling ball not hit the ground at the same time when dropped from the same height? The feather experiences significantly more air resistance relative to its weight than the bowling ball does, causing it to fall slower.
Gravity and Air Resistance
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Terminal velocity: The constant speed that a freely falling object eventually reaches when the resistance of the medium prevents further acceleration.
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What term means that the force of air resistance equals the force of gravity? Terminal velocity.
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A skydiver is falling to Earth and opens his parachute. Explain how the force of air resistance changes from the moment the parachute opens. When the parachute opens, the surface area increases significantly, causing a considerable increase in air resistance. This force quickly exceeds the force of gravity, resulting in a decrease in the skydiver's acceleration and eventually leading to a slower, steady descent (terminal velocity).
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