Find out how you can defy gravity and cause objects to roll uphill.
What You Need :
- A lightweight cylindrical container (like a plastic storage jar or beaker)
- Rubber bands
- A lump of plasticine
- A tray and a some books to make a ramp where you can adjust the steepness.
What To Do :
1. Put some rubber bands around the beaker or storage jar to give it some grip on your ramp.
2. Build a simple ramp. Rest one end of your tray on the ground and the other end on a pile of books. You might need to adjust the steepness to get this experiment to work.
3. Roll a piece of plasticine so it is the same length as your container.
4. Stick the placticine down one side of the container. Now you're ready to roll!
5. Put the container on the ramp with the plasticine at the top.
6. Roll the container about a quarter of a turn, without letting go of it.
Now let go of the container. You'll see that it rolls up the ramp until the plasticine is at the bottom of the beaker. Spooky huh... Or is it?
img src="/spark/experiments/img/uphill05.jpg" border="0" alt="Diagram to explain how it works">
Whats Going On:
The container may appear to be defying the laws of gravity when it rolls up the ramp, but it's not. What we are seeing is how gravity and an object's centre of mass or balance work together.
Every object has a centre of mass, the point that it would balance on. When the beaker is empty, its centre of mass or gravity is in the centre of the container. If you placed it on the ramp, gravity would pull through the centre and the beaker would roll down to the floor.
The plasticine is heavier than the container, so when it's added to the beaker the centre of mass changes to where the plasticine is.
By putting the container on the ramp with the plasticine at the top, you were also pointing the centre of mass at the top too (step 1). And while your beaker rolled up the tray, the centre of mass actually rolled downwards (step 2).
So the laws of gravity still hold true!