Friction When the arrow flies from the bow, it eventually slows down, falls down and stops. When a ball is thrown into the air, it eventually stops going up and starts coming back down to the ground where although it might bounce a few times, it eventually stops. When you ride down hill on your bike and you want to stop before you hit the wall, you squeeze the brakes and eventually, good maintenance assumed, you stop. When the wind blows the sails the boat will move through the water. When the wind stops blowing, the boat will eventually stop What has surface got to do with friction? What has shape got to do with friction? What is friction? What is actually going on when the arrow stops, the balls drops or you don’t actually hit the wall?

Useful Words Friction Air and water resistance Equilibrium Force meter Vocabulary Useful Words Friction The action of one push or pull acting against another push or pull where the result is fast transfer of energy spilling into heat and sound Air and water resistance The push back of air or water as an object goes through. This depends on the shape of the object. Stillness. All the directions of pushes and pulls on an object are balanced so the object stays still Equilibrium Force meter Used to measure force in Newtons Newton A unit of force needed to lift or otherwise move a mass of 100 grams (approximately) Equilibrium Stillness: the balance of all forces on an object Previous

Force meters 3 Newtons 7 Newtons 5 Newtons 8.5 Newtons Previous

Forcemeter reading in Newtons Using Force meters Try hanging different objects from around the classroom on the force meter. Write down the readings you get! Idea for starting and investigation Object Forcemeter reading in Newtons Previous

Force against resistance A stationary object is at equilibrium. The gravity pull down force is the same as the opposing push up force of the surface. Equilibrium means balance or equal. A push force from the side will move the object but the ease of movement depends on the roughness or the smoothness of the surface. This means the surface causes more or less resistance : greater or less friction or grip. More force is needed to start the movement on any surface than is need to keep it moving. The effort depends on the type of sliding surface Previous

Investigation: Which surface do objects slide on most easily? Which of these surfaces will a weighted box slide across most easily? A) Vinyl B) Wood C) Carpet When you have chosen, explain why you think this surface will be the easiest to slide across. Make a careful note of the amount of force being applied just before movement takes place. Previous

Investigation (cont.) Investigation: Devising a fair test and persevering. Example: Investigate the force needed to move an object over a given distance on a range of surfaces. The brief says an object over a range of surfaces so we need to list the variables and eliminate those we don’t need. Variables here are surface, object, weight, distance, slope and force We keep things simple by: Making a standard weight e.g. 1kg is approx 10 newtons Using a flat surface Using a standard distance e.g. 20cm The only variable now is the type of surface. Now we can make a prediction and test the measurable element: the newtons required to start and to continue the movement. Previous

Tyres on a car Playground slide Goalkeeper’s gloves Shoe laces High and Low Friction Is it best for each of the following to have a rough or a smooth surface? Situation High Friction Low friction Tyres on a car Playground slide Goalkeeper’s gloves Shoe laces A drawer Ice skates Climbing rope Previous

Which shape do you think will travel through the water the quickest? Water Resistance Which shape do you think will travel through the water the quickest? Why do you think this one will be the quickest? Test different shapes to see how quickly they move through the liquid. Previous

Water Resistance movement water Previous

Friction: the collision of opposing forces brakes ice skates Rough: high friction Smooth: low friction tyres slide goalkeeper’s gloves drawers Friction: the collision of opposing forces Air resistance- the opposing push of air molecules against on an object moving through air Water resistance- the opposing push of water molecules against on an object moving through air Big area: High resistance Non streamlined: High resistance Streamlined: Low resistance Small area: Low resistance dart streamlined car sail (boat) parachute person walking through water submarine fish boat Previous Beginning