13.2 Gravity and Motion
What does the word "centripetal" mean?
"toward the center"
What two motions form an orbit?
1. moving forward 2. free fall
What is the rate at which a falling object accelerates to Earth?
9.8 m/s/s (meters per second squared)
Why is it incorrect to say a sky diver is in "free fall"?
A sky diver has air resistance as he/she falls, so there is another force acting on him/her besides gravity.
What is free fall?
A term used to describe when the only force acting on an object is gravity.
If you want to shoot an arrow at a bull's eye, where do you have to aim?
Above the bull's-eye
Why do objects of the same size and shape fall to the ground at the same rate?
Acceleration due to gravity is the same for all objects.
Suppose a baseball and a marble are dropped at the same time from the same height. Which ball would land first according to Aristotle? Explain.
According to Aristotle, the baseball would drop first. He thought the rate at which an object falls depends on its mass.
Suppose a baseball and a marble are dropped at the same time from the same height. Which ball would land first according to Galileo? Explain
According to Galileo, they would both land at the same time. He thought that the mass of an object does not affect the time the object takes to fall to the ground.
What is a vacuum chamber?
Containers from which most of the air has been removed.
What is the downward motion of the space shuttle in orbit called? Why?
It is called free fall because gravity pulls it toward Earth (no air resistance).
How does gravity affect the solar system?
It maintains its shape by keeping the planets orbiting around the sun
If there were no gravity, what would happen to a space shuttle?
It would continue in a straight line instead of orbitting
What will happen if you aim at a bull's-eye on a target?
The arrow will hit below it.
Why does a crumpled paper fall faster than a flat paper?
The crumpled pair has less air resistance
What is projectile motion?
The curved path an object follows when it is thrown or propelled near the surface of Earth.
If a feather and an apple are dropped from the same height in a vacuum chamber, what will happen?
They will both fall with the same acceleration, and land at the same time, because there is no air resistance and both are in free fall.
If a golf ball and a table tennis ball are dropped at the same time from the same height, which will land first? Explain.
They will land at the same time because they will fall at the same rate.
When is an object orbiting?
When it is moving around another object in space.
Where can free fall only occur?
Where there is no air, in a vacuum.
If you want to hit a target, where do you have to aim?
You have to aim above it.
What term describes how quickly velocity changes?
acceleration
What is the term used to describe the force that acts against the motion of objects through the air?
air resistance
What two forces combine to determine the net force on a falling object?
air resistance and gravity
When the space shuttle follows the curve of the Earth, what is that path called?
an orbit
What are examples given of projectile motion?
bullfrog jumping, swimmer diving, water spraying from a hose
What kind of force does gravity provide on the planets?
centripetal
What two movements make up orbiting?
forward movement and free fall
What gives an arrow shot horizontally from a bow its vertical movement?
gravity
What makes the paths that planets follow elliptical?
gravity
What provides the centripetal force to keep things in orbit?
gravity
If there were no air resistance, what would happen to hailstones which have a terminal velocity between 5m/s and 40m/s depending on their mass?
hailstones would hit the ground at velocities near 350 m/s--a danger to people, houses, cars
What two movements combine to form projectile motion?
horizontal and vertical mvoements
After a thrown ball leaves your hand, what happens to its horizontal velocity?
it accelerates downward
How does gravity maintain the orbits in the solar system?
it keeps them moving around the sun by providing a centripetal force
What does a centripetal force do?
it makes things move in a circular path
What kind of shape is an ellipse?
nearly circular or oval
What is terminal velocity?
the constant velocity of a falling object when the force of air resistance is equal to the magnitude and opposite in direction to the force of gravity
After a ball leaves a pitcher's hand, what happens to a) the horizontal velocity b) the vertical velocity?
the horizontal velocity remains constant, the vertical velocity increases because gravity causes it to accelerate downward
What happens when the upward force of air resistance equals the downward force of gravity?
the object stops accelerating and reaches its terminal velocity
Name three things that are kept in place in the solar system due to gravity.
the planets (orbiting around the sun), the moons (orbiting around the planets), the rings of Saturn (tiny pieces of ice and dust orbiting around Saturn)
What three factors determine the amount of air resistance on an object?
the size, shape, speed of the object
What is centripetal force?
the unbalanced force that makes things move in a circular path
What are everyday shapes that are shaped like ellipses?
watermelons and footballs