# Forces

### A guide to what we have covered during this topic....

## The basics

- Forces can either be '
**push**' or '**pull**', and they work__in pairs__(*have a look at the diagram below).* - Forces are also either
**balanced**or**unbalanced,**and they are measured using**Newtons (N)** - The
**magnitude**of a force is shown on a diagram by the**size of the arrow**

## What are the pairs of forces on this diagram?

**REACTION - WEIGHT are a pair****DRAG - THRUST are a pair**

__Can you identify which forces are push, and which forces are pull?__

- The car is not moving,
**OR...** - If its already moving then it will stay at a constant speed.

## How do we make an object move?

**Make the forces unbalanced!**When forces become**unbalanced**and object will move, this movement includes acceleration (speeding up), decceleration (slowing down), changing direction.- When this guy jumps out of the plane the forces on him become
**unbalanced**, and he changes direction and speed.

## How do the forces change as you jump out of a plane?!

**GRAVITY**

Gravity is the force that pulls you down towards the Earth, *but what is gravity?*

- A force that attracts objects with mass towards each other.
- Any object with mass (KG) creates gravity
- The more mass something has, the stronger the gravitational pull it has.

The skydiver has mass (KG) and so he has his own gravitational field, but because the Earth has a much bigger mass it pulls him downwards (really fast!).

## The difference between Mass and Weight (follow the link below)

## How much would your WEIGHT be on other planets? Use this calculator to find out....

**MASS**(how much matter/stuff your made of) doesn't change on other planets, but

**WEIGHT**does. This is because

**WEIGHT**depends on

**GRAVITY,**and gravity changes on different planets because each planet has a different

**MASS**(remember how we said that gravitational strength depends on how much

**MASS**there is)

## Density

## Why are there layers in this picture?

Density is how much **MASS** there is in a specific **AREA**. For example, the density of water is **1.0g/cm2**.

**g=MASS****cm2=AREA**

**Honey **is the substance with the** highest density**, and** lamp oil **has the** lowest density.**

## You can calculate DENSITY using this handy formula triangle

## Practise Questions

*A block of wood has a density of 0.6g/cm3, and a volume of 1.2 cm3, what is the mass?*

*An 800g boulder has a density of 8g/cm3, what is the volume?*

## Pressure

**F = FORCE****p=PRESSURE****A=AREA**

## Example Questions

**N**and wearing shoes with an area of 0.2

**m2**, what pressure does he exert?

A birthday present has an area of 2m2 (2 metres squared), and exerts a pressure of 20N/m2 (Newton metres squared), how much does it weigh?

## Moments

**moment**is a

**turning force**that acts around a

**pivot**(think of how a see-saw moves).

See if you can identify where the pivot is in these diagrams below....