Newton's 3 laws on getting hit by an apple...

A physicophical view point... (Get it?)

If Yoshi does it, you know it has to be cool.

1. Inertia.  Objects are lazy. So it wants to keep doing whatever it is doing unless there is an external force affected on it. Ex. A ball in space will keep flying, it doesn't want to stop because it is lazy.
2. F=ma.  Since force is positively related to acceleration, and mass is negatively related to acceleration, the equation F = ma can be formed (a = F/m is another form of zis)
3. For every action force, there is an reaction that is equal in the completely opposite direction. When you punch a wall, the impact sends the force into the wall and into your fist. That is why you get hurt. :)

The various applications for the Newton's 3 laws can be divided into 4 sections:

1) Equilibrium

This diagram increases the tension dramatically...

When there is completely no motion, and everything is in a state of balance, this is called equilibrium. Usually, you are required to find the tension or the mass of the object. The vertical component of the system is usually Fg which is the force of gravity (also = mg). There is also usually the two tensions given. You should know that T1y + T2y = Fg since all forces should negate each other.

When dealing with these questions, it is essential for you to state your assumptions, this way, the reader will understand your viewpoints.

Assumptions:

- Friction = 0

- Acceleration = 0 (No motion)

- Total Force turns out to be 0

- (If there is tension then T1x = T2x)

- Set positive axis

- No air resistance
- No movement at all

2) Incline

Ramping up the difficulty...

When an object is at a state or rest or moving on a surface that is not horizontal. The only new component about this is the force of friction. As previously explored, the force of friction, if not given, is m(miu)Fn (Force of Normal) The usual components in the free body diagram is the gravity (Fg), the force of normal (or surface, = Fn) and friction (f).

When doing these sort of questions, don't forget to set a positive axis (Usually slanted along with the slope of the ramp).

Assumptions:

- Friction cannot = 0

- No air resistance

- Positive axis is usually in the direction of motion

- Fn = Fg, since the object on the ramp is not flying up or down

- Fn is perpendicular to the incline
- No movement in the y-direction

3) Pulley

It really pulls you in..

When an object is pulling or being pulled by another object through tension, it is probably in a system involving a pulley. As you can see, the pulley should consist of a weight on both sides of the wheel thingy thing. Since both ends of the pulley are putting their masses on the string thing, the tension is the same. When doing pulley questions, don't forget to make 2 free body diagrams when required since there is acceleration and forces in different directions

Assumptions:

- No friction on the ropes or the pulley itself

- No air resistance

- a does not = 0

- T1 = T2

- a1 = a2

- Positive axis in the direction of acceleration

- 2 Free Body diagrams
- In some cases, no movement in the x or y - direction

4) Train

All on board the train to physics land....
What do you mean I should get a doctor.....?

Train is basically another word for pulley on a horizontal plane. Search it in the dictionary. No I'm kidding, don't. Anyways... Train is a system where there is 1 force applied to the front of the train, and it drags the other trains using tension. When doing these questions, the easy way to find the acceleration is to consider the whole train as 1 system and therefore finding the total acceleration. This way, you don't have to calculate the tension and substitute like MAD!.
Assumptions:
- No friction, or in other cases yes friction
- No air resistance
- Cables or birds that hit the train have no mass
- Positive axis in the direction of acceleration
- Free-body diagrams according to the number of trains
- No movement in the y - direction
- Acceleration cannot = 0, but is constant


Don't forget, if you don't assume, you will get SCREWED!!!!!

BEWARE THE SCREW!!!