Walk towards the origin slowly, gradually increasing your speed.

Walk away from the origin slowly, gradually increasing your speed.

Walk away from the origin slowly, gradually increasing your speed.

Walk towards the origin quickly, gradually decreasing your speed.

Walk away from the origin quickly, gradually slowing down.

Measured in meters

From the start to the finish (not distance which is the entire path)

In relation to a reference point

If a bus is moving 20 mph and you walk 1 mph to the front, then you ADD the velocities. If you are walking from the front to the back, you subtract

Law of Inertia and car crashes

The more mass you have, the more inertia you have.

Inertia determines the ability to make something stop or change its motion. So, it is easier to change the motion of a baby stoller than it is a school bus.

More mass = more inertia

F = m x a

measured in Newtons

If something is falling or the mass is affected by gravity, you can use

W (weight) = m x g

Why? Weight IS a force due to gravity.

Action and Reaction Pairs

Equal Forces in opposite directions

You hit the wall and it hurts because the wall was hitting you!

If the bug hits a windshield, we are sad that the big died, but the bug put the same force on the windshield that the windshield put on the bug

Object is NOT at rest...look at y axis!

The object is moving at a constant velocity

1. All your old chapter tests that we taped into your notebook

2. The notes on graphing

3. CBA 1 and 2

4. The practice semester exam we did in class yesterday

A lot of the questions are similar or even the same, so please review the old tests and CBAs!!!!!!!!

1. Which object has a greater inertia?

A. 2kg object moving at 6m/s 

B. 3kg object moving at 5m/s

C. 6kg object moving at 0m/s 

D. 7kg object moving at 1m/s

Potential has to do with how high something is

(GPE = m g h) and Kinetic has to do with how fast something is going (KE = 1/2 m v ^2)

Potential is converted to kinetic as an object falls

The potential at the top is 100% and the kinetic is 0%. By the time the object hits the ground, it is moving the fastest, so its kinetic is now 100% and potential is 0%.

work is measured in JOULES

Work = change in kinetic energy

work = force x distance

example: If you walk up the stairs, like in our lab, you walked up a distance of 2.16 meters. We would multiply your force by the distance you went UP from the ground.

What happens if you don't have the force???

Well, you have to do (m x g) to get the force!

The amount of work you do is equal to the change in kinetic energy.

Let's say you drop a 2 kg ball from rest and by the time it hits the floor it was going 10 m/s.

Work = the change in KE

So you have to calculate the KE initially and then the KE from when it hits the ground and then subtract.

momentum before = momentum after

the velocity may change when something is hit that was originally at rest, but their momentum will never change

With projectile motion, when do I use

v = d/t 

With projectile motion, when do I use:

d = vit + 1/2 at²

converted to:

y = 1/2 gt²

If something is falling or being dropped, gravity is a factor, so you would use g = 9.8 instead of solving for "a".

For example, if you are lifting a 20kg dog 3 meters and want to know the work:

w = f x d

w = m x g x h

w = 20 kg x 9.8 x 3 m

A 5kg box is being pushed with a force of 20 N up a 10m ramp that is 4m off of the ground. How much work would be done to lift the box to the top?

Since work = force x distance,

W = 20 N x 4 m = 80 J

You don't use the mass because we already know the force (and don't need to do f = m x g to get it) and we want to know how high the box was lifted, not how long it was pushed, so we don't use the 10 m.

400 m west

Why?

He is walking in two different directions, so you subtract.

Alex throws a football off the top of the school to a friend below. He throws the ball at 2 m/s. The school is 10 m high. How much time does it take for the ball to hit the ground?

Remember, time to launch (horizontally) equals time to drop (vertically).

So, you can use y = 1/2 g t²

10 = 1/2 (9.8) t²

t²=2.04

square root both sides

t = 1.43 s

What is the impulse of a 10 N force acting westward on a car for 5 seconds?

 Impulse = force x time

10 n x 5 seconds = 50 N s westward