# Gravity and Motion

What did Galileo prove?

The mass of an object does not affect the rate at which it falls. The mass does not affect the rate of acceleration.

Why do objects fall to the ground at the same rate?

because acceleration due to gravity is the same for all objects.

What is the rate of acceleration due to gravity?

9.8 m/s/s

What formula do you use to find the velocity of falling objects?

v = gt

What is air resistance?

a fluid friction (goes in the opposite direction) that opposes motion of objects through the air. Air resistance acts in the opposite direction of gravity.

What keeps an object accelerating?

Net force

What does the amount of air resistance depend on?

the size and the shape of an object.

Which has more air resistance: a sheet of paper or a sheet of paper crumpled into a ball.

the sheet of paper has more air resistance because it has a greater surface area and a greater fluid friction.

What happens to the force of air resistance as an object accelerates?

the force of air resistance keeps increasing

What is terminal velocity?

when the force of air resistance is equal to the force of gravity and the net force is zero. the object no longer accelerates as it falls because the size of the force upwards (air resistance) matches the size of the force downward (gravity). Is a result

What happens when net force = 0

the object continues falling, but it no longer accelerates.

When does free fall occur?

When there is no air resistance (in a vacuum or in space). Gravity is the only force acting on the object.

What two motions combine to form an orbit?

Forward motion and free fall

What does gravity provide?

the unbalanced force that keeps planets in centripetal motion.

What is projectile motion?

the curved path an object follows near the Earth's surface.

What two components combine to from projectile motion?

constant horizontal motion and vertical motion.

If there is no air resistance, would a brick or a small flat pebble land first if dropped?

they would land at the same time.

Why does the force of air resistance increase as an object accelerates towards the ground?

because fluid friction increases as the object moves faster.

Why is the unit for acceleration due to gravity m/s/s?

because acceleration equals the change in velocity divided by time?

What is newton's first law of motion?

an object at rest remains at rest and an object in motion remains in motion at a constant speed and in a straight line unless acted on by an unbalanced force.

When does an object start moving?

when an unbalanced force (a push or a pull) is exerted on it.

According to Newton's first law, Why does an object eventually stop?

because friction provides the unbalanced force that makes it stop?

What is inertia?

the tendency of all objects to resist any change in motion. objects will remain at rest due to inertia and objects will remain in motion due to inertia. Inertia is why it is impossible for a bike or a plane to stop instantaneously.

_______ is a measure of inertia.

Mass. a small mass has a small inertia and a large mass has a large inertia. It is harder for objects with more inertia to stop.

What is Newton's second law of motion?

the acceleration of an object depends on the mass of the object and the amount of force applied.

What does acceleration depend on?

mass. For the same force an object's acceleration increases as its mass decreases and its acceleration decreases as its mass increases.

What is acceleration also dependent on?

force. An object's acceleration increases as the force on it increases and vice versa. If you want two different objects to accelerate at the same speed then you have to apply a larger force to the object with a larger mass.

What is the formula for newton's second law of motion?

F=ma

What is Newton's third law of motion?

Whenever one object exerts a force on a second object, the second object exerts and equal and opposite force on the first.

All forces act in ______

Pairs

According to Newton's third law, what happens as you push on an object?

The object pushes back on you. The force that you apply is equal to the amount of force the object is pushing back on you. The only different is that it acts in the opposite direction.

According to Newton's third law, what occurs when you walk?

You exert a backwards push on the ground (the action) which causes the ground to push you forward (the reaction).

Why doesn't the force you exert on the Earth cause the Earth to move?

Because the Earth has a huge amount of inertia and the force you exert is way too sank to move it. However, the force that the Earth exerts back on you propels you forward.

How is momentum similar to inertia?

Momentum is similar to inertia because it depends on mass. However, momentum is dependent upon velocity.

Objects in motion have _____________

momentum

What is another name for Newton's first law?

the law of inertia

Does a Jeep have more momentum than a mini cooper if they are moving at the same speed?

yes

Does a Hummer going 65 mph have more momentum or does a Hummer going 50 mph have more momentum?

a Hummer going 65 mph.

What is the formula to calculate momentum?

p=mv

What happens to the momentum during a collision?

the momentum is transferred from one object to another during a collision. As two objects collide, the momentum of the first object is transferred to the second object and the momentum of the second object is transferred to the first object?

What happens to the total amount of momentum before and after a collision?

It stays the same

What is the Conservation of Momentum explain?

It explains that although the momentum of two objects are transferred to one another during a collision, the total amount of momentum stays the same before and after the collision.

According to Newton's first law of motion, why should you always wear a seatbelt.

because your body does not stop instantaneously; when the car stops, your body will continue to move.

If a ball is at rest on the floor of a car moving a constant velocity. What will happen to the ball if the car swerves suddenly to the left.

It will go right.

How much force is being applied to an object that is moving at a constant velocity?

zero, because it is not speeding up, slowing down, or changing direction.

Jim says My force will produce an opposite and cancel my effort so why should I push a box?

because his force is greater than the force of friction, so the box will move.

an inflated balloon is released and moves by shooting across the room. Explain how this works.

the force that the air in the balloon is exerting is enough to propel it forward.

How does increasing the speed of an object change its momentum?

the momentum will increase because the velocity is increasing.

During a race, you double your velocity. How does that change your momentum?

How does the final speed of the two train cars after a collision compare with the initial speed of the moving train cars before the collision?

Your speed decreases the momentum is transferred.

how do newton balls illustrate the Conservation of Momentum?

because the balls transfer momentum during the collisions.

Momentum

A property of a moving object that depends on an object's mass and velocity

parachutes slow skydivers to a safer terminal velocity because parachutes

increase air resistance

as long as the net force of a falling object is not zero, the object

accelerates downwards

because of projectiles motion, when aiming at a target you should always aim

above the bull's eye

the downward acceleration of a thrown object in projectile motion is

identical to that of a vertically falling object regardless of the horizontal part of the projectile motion.

Why do planets stay in orbit around the sun?

because unbalanced forces act on them, two motions combine to cause orbiting, and the sun's gravitational force provides a centripetal force on the planets.

Centripetal force on an object acts in the

same direction as gravitational force

astronauts float inside space because

they are in free fall

if one object is in projectile motion and the other is not which will land first if dropped from the top of a building?

they will land at the same time because projectile motion does not change the acceleration due to gravity.

if you through a ball into space, how much force is needed to keep the ball moving at a constant velocity.

None

If the force of gravity stopped acting on the planets, in what kind of path would the planets move?

a forward motion