Year 7 | Physics

Forces 

A force is something that can cause a change in movement or shape of an object, and can be a push, pull, or a twist. 
Forces are important because they are important for changes in motion. If something moves, it is because a force has acted on it. 
Forces can: 

  • Start something moving, or speed it up 

  • Stop something moving, or slow it down 

  • Cause an object to change direction 

  • Cause an object to change shape 
     

The unit of measurement for force is called the Newton (N). 
Newtons are measured using a spring balance 
It takes about 1N to lift an apple 
 

Balanced Forces: Two forces working in opposite directions at the same strength. No change in motion. 
Unbalanced Forces: Two forces working in opposite directions not the same strength. Results in a change of motion 

Net Force Diagrams 

  • Forces acting on an object can be shown with arrows – the size of the arrow is relative to the amount of force applied 

  • Arrows pointing towards the object indicate pushing 

  • Arrows pointing away from the object indicate a pulling force 

  • Numbers can be used to indicate exactly how much force is being used 

  • Resultant force is referring to the amount of force after working out the amount of N 

Friction 

  • Friction is a kind of force 

  • Friction acts to slow objects down 

  • Friction acts whenever two objects are in contact with each other 

  • Friction is known as a “contact force” 

  • Friction works against motion and movement 

How it works 

  • Friction happens because of very small bumps that exist on all surfaces – even smooth looking surfaces like glass 

  • When two surfaces rub against each other, the bumps catch and grab at each other, this slows the motion down and causes friction 

What affects friction? 

  • Friction depends on how rough the surface is 

  • It also depends on how hard the surfaces are pushed together 

  • So, ice is very slippery because of how smooth it is 

Good and bad friction 

  • Good - Walking, pushing your foot backwards against the ground pushes you forward. If there is no friction, your foot will slip 

  • Bad – Friction against two objects can wear them down, making them thinner and weaker, like car tires. Friction between an object and air slows the object down because of air resistance or drag. 

Reducing and increasing friction. 

  • Reducing – Rolling wheels produce less friction compared to pushing. Hovercrafts travel on a blanket of air instead of being in contact with the ground or water. Lubricants like oil reduce friction as well. 

  • Increasing - The heavier an object is, the more friction there is between the object and the floor, therefore, it is harder to push. 

Glossary of Terms 

  • Force 

  • Newtons (N) 

  • Spring Balance 

  • Balanced force 

  • Unbalanced force 

  • Net force diagram 

  • Resultant force 

  • Friction 

Simple Machines 

Reduce the amount of work needed to do something and gives you a mechanical advantage. 

Examples: 

  • Lever 

  • Pulley 

  • Inclined Plane 

  • Wedge 

  • Screw 

  • Gears 

The amount of force you need to get the job done is load. 

Simple machines can: 

  • Change the size/amount of force 

  • Make things speed up 

  • Change the direction of a force 

Changing the size of a force: Machines can be used to decrease the amount of effort needed to get the job done. They do this by magnifying the force that you apply. 

Making things speed up: Machines can make things move faster than normal. You need to put in more effort to get them going, but then they can go faster. Gears. 

Changing the direction of a force: For example, you pull down on a cable to pull blinds up. 

Mass vs Weight 

Mass: Mass refers to the amount of matter in an object, it is measured in kg, g, tonne etc. 
Weight: Weight refers to the effect of gravity on an object. It can change depending on where you are. 

Gravity 

Gravity is a pulling force of attraction 
The more mass an object has, the greater the pulling force between it and another object will be. Everything with mass has its own gravitational pull! Earth has more mass and more gravitational pull than you, so you get pulled to it instead of you pulling Earth to yourself.  
Gravity acts without objects having to physically touch, so gravity is known as a non-contact force.