(Gennie Gleeson, Grade 3, St Augustine's, Baxter)

Distance, Speed & Road Safety

Worksheet: There is a worksheet for them to create their own superhero: Superhero worksheet

Motion Activities:

Distance

Distance is measured in Standard International Units in metres (m).

Speed

d

Acceleration

d

Measuring motion

d

Friction on the road

Tyres grip the road by friction and that is what allows a driver to control their car. There is a large amount of friction between the tyres and the road so that the tyres can grip the road well. Then:

Brakes work on friction too. There is a set of brake pads on each of the car's wheels. When the driver presses on the brake pedal, these brake pads press on the metal discs fitted behind the wheel. This produces friction between the pads and the discs, making the wheels slow down. If the friction between the tyres and the road is reduced, driving becomes dangerous. That's why drivers have to take great care when driving on icy roads. Driving on wet roads also needs extra care. The water acts as a lubricant between the tyres and the road ad makes braking more difficult. The pattern of grooves is designed to let water escape from underneath it.

If the driver of a car travelling at 80 km per hour wants to stop the car it will take 16 metres to act on it and press down on the brake pedal. It will also take the following distances to actually stop...

35m
70m

Let's go faster

To make a bicycle go you have to supply a force. You push on the pedals and this force turns the wheels. With your first push, the bicycle moves off. As you keep pedalling the bicycle speeds up. A force can make something start to move and then speed up. The bicycle does not keep going faster and faster as you keep pedalling. Instead it reaches a steady top speed and then you have to keep pedalling to keep it at this speed. You are using force without changing the speed. Why doesn't the bicycle go faster and faster? It is mainly due to friction. Two types of friction hold you back when you are cycling. The first type is the rubbing of moving parts: the wheel and axle. The second is caused by air resistance. You have to push your way through the air and it increases in difficulty the faster you go. At low speed the friction is small so that the pedalling force goes mainly to speeding the bicycle up. As the speed increases, the friction increases. Eventually the pedalling force equals the forces of friction and these balanced forces keeps the bicycle moving at constant speed. There would be no friction due to air resistance only in space.