1. Friction

2. What is friction?  an outside force that happens when two things rub together.  It opposes the motion of an object  If there were no friction we would have perpetual motion. perpetual motion perpetual motion

3.  Friction is low if the surfaces are smooth and wet;  Friction is high if the surfaces are dry and rough;  Friction causes heat;  Friction can be reduced by using lubricants, ball bearings, air-cushions and by streamlining

4. website  We need friction. Imagine life without it - everything would slip and slide about. We need friction between our feet and the ground else we would not be able to stand up. We need friction between our car tires and the road else we would skid and crash. And imagine if there was no friction between our brake pads and the wheels…see above

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6.  Causing heat to build up is not always a good thing, especially inside a car engine. Oil is used to lubricate the parts of a car engine so that it runs smoothly. The oil makes the surface smoother so there is less friction, less wear on the metal and hence less risk of fire.

7. Friction can make things hot. Remember how cavemen made fire by rubbing two sticks together?

8.  There are two main types of friction:  1. Static friction: the frictional force that opposes any attempt to move a stationary object along a surface.  2. Sliding friction: (sometimes called "kinetic" friction): this frictional force opposes the sliding motion of two surfaces rubbing together.  A third type of friction, rolling friction, is a special case of static friction

9. Air resistance  the frictional force from the air that resists the forward motion of the object  Type of fluid friction

10. terminal velocity  an object falling towards the earth, in non-vacuum, is the speed at which the gravitational force pulling it downwards is equal and opposite to the atmospheric drag (also called air resistance) pushing it upwards  Falls at a constant speed

11. At home activity  Stack of coins activity  Make a stack of ten 2p pieces on a smooth surface. Do you think you can remove the bottom coin without knocking the stack over?  You will need:  Ten 2p coins  Butter knife  Smooth surface

12. What to do:  Make sure your stack is really straight.  Now take a butter knife and place the edge of the knife against the bottom coin.  Give it a quick tap and the coin should shoot out the side of the stack and leave the rest standing.  How tall a stack can you make? Will it still work? What happens if you tap the coin slowly?

13. science friction... A deserted street, West Berlin, 1971, freezing snowy mid winter.

14. Gravity