Frequently Asked Questions: Forces

Q. Why does a diver dive with his hands clasped to form a more stream-lined shape? Why do belly-flops hurt more than diving with your arms outstretched in front of your head? Why do diving pools have a fountain at the surface of the pool?
A. Water has an array of interconnecting attractive forces between the water molecules at the surface. This is called cohesion and also surface tension. The surface tension can be broken by two methods - piercing it with a small object (e.g. your pointed clasped hands or a fountain) or by using detergents. If a diver did not do these things, it would hurt severely or he/she would be knocked unconscious by impact with the water surface.

Q. How does paper towel soak up water?
A. There is an attraction between the water molecules and the paper molecules called adhesion. There is an even greater attraction if the fibres form thin tubes within the paper towel.

Q. Why are raindrops spherical?
A. The water molecules are quite strongly held together in all directions by forces called cohesion.

Q. Why are oil droplets smaller in diameter than water droplets?
A. Oil has a greater attractive force (called cohesion) holding its molecules together than does water.

Q. Why does glue stick to paper but not to the plastic container?
A. There are greater attractive forces (called adhesion) between glue and paper than there are between glue and plastic.

Q. Why does a rifle-shooter hold the gun firmly against his shoulder when firing?
A. For every action, there is an equal and opposite reaction. As the bullet leaves the barrel of the rifle (action), the rifle kicks back or recoils against the shooter's shoulder (reaction). If he/she did not hold the rifle firmly, the result may be a fractured shoulder.

Q. What effect would a fly 'splatting' on the windscreen have on the movement of a car?
A. The forces of an impact between a car going in one direction and a fly going in another direction affect both. Both will be slowed to a minor extent in the case of the car, and to a major extent in the case of the fly.

Q. Who invented the first parachute?
A. Probably Leonardo da Vinci.

Q. Where does the 'rubber' go from worn tyres?
A. The synthetic 'rubber' of tyres goes onto the road surface and into air as dust.

Q. Why do you put chalk on the tip of a snooker cue?
A. It gives more grip or friction when it hits the ball for more accuracy.

Q. Why do vehicles driving on snow-covered roads wrap chains around their tyres?
A. The chains give more grip or friction with the slippery roads.

Q. Why does an archer aim higher than the bulls-eye in order to hit it?
A. They are compensating for the force of gravity.

Q. Why are golf balls dimpled?
A. They are more aerodynamic than smooth balls.