# Mechanics AS Physics.

These are the key points for the mechanics unit of AS physics

- Created by: Billy Radford
- Created on: 26-05-10 13:27

First 391 words of the document:

Mechanics.

Scalars and vectors.

1. A scalar has only magnitude. Examples include mass, temperature, time, length, speed

and energy.

2. Vector quantities have both magnitude and direction. Examples include displacement,

force, velocity, acceleration and momentum.

To add vectors, calculate resultant forces or calculate resultant velocities you use Pythagoras

theorem and trigonometry.

It is useful to resolve vectors, resultant forces, into horizontal and vertical components.

Motion with constant acceleration:

There are 4 constant acceleration equations. Learn them.

Acceleration is equal to change in speed divided by time.

Speed equals distance over time.

Free fall and projectile motion.

Aristotle thought that if two objects of different mass where dropped from the same height

then the heavier one would hit the ground first.

Galileo thought that all objects should accelerate towards the ground at the same rate

therefore objects of different weights should hit the ground at the same time and the reason

this was not the case was air resistance. Galileo's theories were generally accepted.

Free fall is defines as "the motion of an object undergoing an acceleration of "g".

For objects in free fall you can replace acceleration with "g".

For projectile motion you have t take the vertical and horizontal components separately.

For the horizontal motion there horizontal motion is not affected by gravity or any other forces

so it acts as a constant speed. Therefore you can use speed equals distance divided by time.

If the object starts off at angle:

1. Resolve the initial velocity into vertical and horizontal components.

2. Use the vertical component to work out how high and long it is in the air for.

3. Use the horizontal component to work out how far it goes whilst it is in the air.

Terminal Velocity is when the force of weight is equal to the force of air resistance so there

is not net force and there is no acceleration.

Displacement time graphs.

The gradient of a displacement time graph tells you the velocity.

A curved displacement time graph means acceleration:

1. The greater the gradient of the curve the greater the acceleration.

2. The smaller the gradient the smaller the acceleration.

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