### Galileo

He argued that the mass of an object does not affect the time the object takes to fall to the ground.

### Objects fall to the ground at the same rate

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

### If an object hits the ground with a velocity of 98 m/s, how long did it take to reach the ground

10 seconds.

### If an object hits the ground with a velocity of 49 m/s, how long did it take to reach the ground

5 seconds

### free fall

This occurs only if gravity is pulling down an object with no other forces acting on it. It is usually accompanied by the playing of a Tom Petty song. :)

### two places there is no air

space and a vacuum. A third place is also potentially inside an 8th graders brain. :)

### terminal velocity

the constant velocity of a falling object when the force of air resistance is equal in magnitude and opposite in direction to the force of gravity

### why is terminal velocity a good thing

because if there was no maximum speed, things like hailstones would destroy everything in their path.

### Why does the moon stay in orbit

because the Earth's gravitational force provides a centripetal force on it.

### projectile motion

the curved path that an object follows when thrown, launched, or otherwise projected near the surface of Earth

### leaping frog, water sprayed by a sprinkler, an arrow shot by an archer

These are all examples of projection motion.

### If a rock at rest falls off a tall cliff and hits the valley below after 3.5 s, what is the rock's velocity when it hits the ground?

34.3 m/s downward

### Newton's First Law of Motion

Objects in motion will remain in motion unless acted upon by another force.

### inertia

the tendency of an object to resist being moved or, if the object is moving, to resist a change in speed or direction until an outside force acts on the object.

### Newton's Second Law of Motion

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

### Why do newer cars pollute less than older cars?

They have less mass, so it requires less force to move them.

### What is the acceleration of a 3 kg mass if a force of 15 N is used to move the mass? Note: 1 N = 1 kg×m/s

5 m/s

### What is the acceleration of a 4 kg mass if a force of 16 N is used to move the mass? Note: 1 N = 1 kg×m/s

4 m/s

### What is the acceleration of a 3 kg mass if a force of 18 N is used to move the mass? Note: 1 N = 1 kg×m/s

6 m/s

### What is the acceleration of a 2 kg mass if a force of 18 N is used to move the mass? Note: 1 N = 1 kg×m/s

9 m/s

### Newton's Third Law of Motion

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

### Space shuttle action and reaction force pairs

Thrusters pushing the exhaust games downward as gases push the shuttle upward with equal force.

### Action and reaction forces example

A rabbit's legs exerting a force of Earth with Earth exerting an equal force on the rabbit's legs causing the rabbit to accelerate forward.

### Equal and opposite force

whenever an object exerts a force on another object, the second object exerts this...

### What is the momentum of a ball with a mass of 120 kg that moves with a velocity of 16 m/s?

19,200 kg m/s

### What is the momentum of a ball with a mass of 100 kg that moves with a velocity of 16 m/s?

16,000 kg m/s

### What is the momentum of a ball with a mass of 200 kg that moves with a velocity of 16 m/s?

32,000 kg m/s

### What is the momentum of a ball with a mass of 200 kg that moves with a velocity of 12 m/s?

24,000 kg m/s

### What is the momentum of a ball with a mass of 100 kg that moves with a velocity of 12 m/s?

12,000 kg m/s

### What is the momentum of a ball with a mass of 150 kg that moves with a velocity of 12 m/s?

18,000 kg m/s

### law of conservation of momentum

this means that anytime objects collide, the total amount of momentum stays the same.

### when does the law of conservation of momentum apply

then objects stick together or bounce off each other after they collide.

### If a fast moving car has a greater velocity than a slow moving car....

a larger force is needed to stop the faster moving car.

### Objects sticking together

After this happens, they move as one. the masses of the objects remain the same. The velocity changes. total momentum before and after collision stays the same.

### Objects sticking together - examples

When one football player tackles another player or when a dog catches a ball.

### Objects bouncing off one another - what is happening

Momentum is transferred from one object to another object.

### Objects sticking together - what is happening

The mass of the combined object is equal to the mass of the two objects added together. Together, the one object has a velocity which is different from the velocity of the two individual items.

### When a cue ball hits a billiard ball.......

the cue ball creates the action force, which makes the billiard ball move.

### What is the reaction force when a cue ball hits a billiard ball.......

this is the equal but opposite force exerted by the billiard ball on the cue ball. It make the cue ball stop moving.