# Physics - Mechanics - Dynamics

Detailed notes that will help when revising for mechanics

- Created by: George Beresford
- Created on: 13-03-12 11:17

First 402 words of the document:

Chapter 3: Dynamics explaining motion

Force and acceleration

To calculate the acceleration produced by a net force we must also know the objects mass

The word equation for calculated the net force is:

Force (N) = mass (kg) x acceleration (m/s^2)

This equation is a simplified version of Newtons second law of motion

It only applies to objects which have a constant mass

From this equation we can see that acceleration is directly proportional to the net Force, and for a

constant Force acceleration is inversely proportional to the mass of the object

Defining the Newton

One Newton is the force that will give a 1kg mass an acceleration of 1m/s^2 in the direction of the

force

1N = 1kgms^-2

Acceleration caused by gravity

If you drop a stone from a distance s, the ball will accelerate towards the ground

This can be shown using a multi flash photograph

The photographs are taken at the same time interval, however the distance between the stone in

the photo's will increase, hence an acceleration

The force causing the ball to fall is the pull of the Earth's gravity (weight)

The centre of gravity of an object is defined as the point where its entire weight appears to act

Without air resistance objects of any mass will fall at the same rate

However air resistance is greater when acting on a lighter object therefore making it accelerate at a

smaller rate

Acceleration of free fall = 9.81 m/s^2

Weight = mass x acceleration of free fall

Acceleration on the moon

The moon is smaller and therefore has less mass and so its gravity is weaker

Because of the smaller effect of gravity the acceleration due to gravity is smaller

Acceleration of free fall on the moon = 1.6 m/s^2

Objects also weigh less on the moon due to the smaller value of acceleration due to free fall

Mass and weight

Mass will not vary from place to place as it is a measure of the amount of matter within an object

Weight will change as it is a force and is affected by the acceleration due to free fall

Acceleration due to free fall is equivalent to the gravitational field strength

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