Aims of this Episode:

• Describe some examples of forces in the world around us;
• Explain the effect that forces can have on objects;
• Define speed and acceleration;
• Explain how forces can alter speed and cause acceleration.

What is Speed?

Simply put, speed is a measure of how quickly you travel a certain distance. 30 mph means that in one hour, you will travel 30 miles; 10 m/s means 10 metres every second and so on…

The faster you travel, the more distance you will cover in a certain time or the less time it takes you to travel a set distance.

How do Forces affect Speed?

Unless you are in deep space there are always forces acting on you. Sometimes these forces balance out (up cancels out down, left cancels right etc.). When the forces cancel out your speed will not change – if you’re stationary, you will remain stationary; if you’re travelling at 30 mph, you will stay at 30 mph.

A simple example would be a bike travelling along the road. As you ride the bike at a steady speed, you know that all the forces are balanced. If you apply the brakes then the force acting backwards increases – there is an overall force (resultant force) – this means that you slow down.

What is Acceleration?

Acceleration means a change in speed*.

Normally we say something accelerates if it gets faster, but weirdly something slowing down is also said to accelerate (in a negative direction). In order for something to accelerate it needs a resultant force (the forces not to balance out).

*On a slightly more advanced note acceleration is not only a change in speed, it can also be a change in direction. Therefore, a resultant force can cause a change in speed or direction.

S@S 018: Forces and Speed
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