Motion---Mechanics

Describes motion and how motion is made.

Two Categories: Kinematics & Dynamics

Velocity is the rate of change of position (v= distance ÷ time.... units meters/second)

Acceleration is the rate of change of speed (change in speed ÷ time.... units m/s^2)

The slope of a distance vs. time graph is velocity; and of velocity vs. time graph is acceleration)

We can show these using vectors which helps us add and subtract. A vector is a magnitude with a direction.

A scalar such as speed and displacement is only a magnitude and no direction.

Newton's Law and Forces

Newton's laws help understand dynamics (what creates motion)

A force is a push or a pull which is measured in Newtons, and is a vector!

We use free body diagrams to determine the direction and find a net force.

If the forces added equal zero that means that there is the same amount of force in

opposite directions for the y direction and the x direction, putting the object in equilibrium.

1) An object in motion or at rest, will stay in motion or at rest unless an outside force acts on it

2)F=ma

2) For every force there is an opposite and equal force

First Law:

For example if you have you Iphone sitting on top of your lap it will remain on your lap but if you accidentally hit your phone, it will move. So your hand provided a force that knocked your iphone which has mass off of your lap.

Now what is acceleration?

So acceleration is the other part to the famous equation F=ma.

F= Force, m= mass, a= acceleration

Acceleration is not the speed of your Iphone but it is the rate at which the speed changed. So your original speed is zero when your iphone is still at rest sitting on your lap. But the second you accidentally hit it then it had a new speed. So to find accerlartion all you have to do it the final speed minus the initial speed which is 0 and divide by the time! It is as simple as that.

So now lets say you are in class and you go to pass your notes to your friend. You push them across the desk (the notebook is in motion) but it stops before it reaches your friend! Doesn't Newtons Law claim that if an object in motion stays in motion unless a force acts on it? So this is the friction force. Some forces are not as obvious so be careful. Friction always is in the opposite direction of motion so will slow down an objects speed.

Second Law:

So when you are sitting on your chair you are putting a force on the chair. Why don't you fall through the chair? Well the chair is also putting a force on you! But what happens if you jump on the chair you still don't go through! That is because the chair's force on you is equal to the force you put on the chair but in the opposite direction. Therefore your forces act as if they cancel out.

Third Law:

This law explains the term Inertia. What is inertia? Well it is the resistance to move. Have you ever gone bowling with your friends and family? Do you prefer to use a smaller ball or a bigger ball? The smaller balls generally have less mass so it is easier to make that ball roll really fast. The larger balls have more mass and are harder to throw fast. That is becase of inertia. An object with a bigger mass needs a bigger force for a large acceleration. So means the ball is more resistant. Resistance to move is interia.