Science -- Your Future, Scotland's Future
SCI-FUN Roadshow Exhibits -- Ball Race
SCI-FUN Roadshow Exhibits -- Ball Race
In this exhibit you learn about how moving objects accelerate and decelerate on slopes.

When a rolling object, such as a ball or something on wheels, goes down a hill it will speed up. When it goes up a hill it will slow down. On a flat surface, it will keep going at the same speed.

The change in speed on slopes is due to gravity. When going downhill, objects will accelerate (go faster), and when going uphill they will decelerate (slow down). On a flat surface, assuming that there is little friction, they will then maintain a constant speed.

So an object that goes down a hill then back onto a flat surface will have increased its speed as it descended. This means it will be going faster along the flat surface at the bottom of the hill than it did along the flat surface at the top. An object that goes up a hill will be going at a slower speed at the top than at the bottom of the hill.

This is because moving up or down a hill changes one kind of energy into another. Objects at the bottom of the hill have more kinetic energy, which means they are moving faster. At the top of the hill, they are higher up, which means they have more potential energy. Moving up a hill converts the kinetic energy into potential energy, and moving down a hill converts potential energy into kinetic energy.

Most of the time, energy is lost and gained in many other ways as well. In models, like the Ball Race exhibit, we tend to remove or ignore friction. In real-life, most moving objects will slow down due to friction. The kinetic energy lost due to friction is converted into heat and sound energy. We can also add energy to a system by pushing or pulling, or using chemical energy, such as burning fuel.

When driving a car up and down hills, we try to maintain a constant speed (normally within the speed limit). To do this, drivers must increase the amount of petrol that goes into the engine when going up hills by pressing the accelerator pedal. This converts the chemical energy of the petrol into kinetic energy. When going downhill, drivers can slow down by reducing the accelerator, so reducing the amount of chemical energy going into the system, or braking, which slows the wheels using friction.

1 When an object goes down a hill it will ________ ________.
2 What causes objects to change speed on slopes?
3 If an object moves along a flat surface, then uphill, then along a flat surface, how will its speed change?
4 What kind of energy does an object have when it is higher up?
5 What two kinds of energy are given out as a result of friction?
6 Can you think of any other kinds of energy?

1 Make a water slide using a slide, a large sheet of plastic and a hose (ask permission first). Tuck the plastic sheet under the end of the slide and lay it out on the grass. Run water down the slide using the hose (this will work without water, but the water reduces friction and makes you go faster). Slide down the slide and along the plastic. How fast are you going along the plastic? Can you slide that fast along the plastic without going downhill first?
2 Watch a ski-jump on TV or the Internet. Draw a sketch of the path of the skier, and try to work out what kinds of energy the skier had the most of at different points in the jump. What kinds of energy are being converted?