Tony McKintosh and Alister Jones, of Kingswell High School, asks :-
What is the physics involved when doing an ''ollie'' on a skateboard?
Gareth Baxter, a skateboarding nuclear physicist at the University of Auckland, responded.
An ''ollie'' is a skateboard manoeuvre whereby the skateboarder and board, from a standing (stationary) start, both leap vertically.
In doing so a skateboarder uses several of the basic laws of physics. The first stage of an ollie is to crouch down and then jump upward, which takes your weight off the board. However, you extend your legs, so that your feet stay touching the board.
This utilises Newton's second law of motion: By exerting a force downward onto the board, a skater experiences an equal and opposite force upward, which temporarily counteracts the force of gravity pressing them onto the board. As soon as their weight is no longer pressing on the board, they push their hind-foot back down again, behind the rear wheels, and lift up their front foot. They're using the back of the board as a lever to lift the front of the board in the air.
The next bit is the trickiest. We now have a skateboard at an angle to the ground, and which isn't carrying any weight except it's own. To get the board off the ground, and into the air, we need to use friction. A skateboard is covered in sandpaper, and the friction between a skater's rubber shoes and the board drags the board in the direction of the motion of the foot. So if you move your feet in a direction parallel to the surface of the board (i.e. upward at an angle to the ground), instead of the foot sliding forward along the board, both foot and board move together and the skateboard leaves the ground.
Of course, you have to do all this in a split second. Explaining it may well be easier than doing it.