Forces 7K

• Mass is the amount of Matter and weight is the force of gravity on the earth
• Pressure is the result of a force acting over an area
• The smaller the area the higher the pressure
• The larger the surface area the smaller the pressure
• Pressure depends on force and area.

  If the force is the same -the larger the area the lower the pressure

  • the smaller the area, the higher the pressure
• Force = Pressure x area

  Area = Force / Pressure

  Pressure = Force / Area
• Friction


  The# force between two touching objects
• Rock climbers


  • Use shoes made from special rubber that increases friction to give good grip
• Downhill skiers


  • Use friction between the bottom of their skis and the snow to control speed
• You should never put oil on bike brakes because adding oil will decrease the friction and the brakes of a bike need alot of friction to stop
• Car owners will regularly replace their car tyres because the friction can eventually wear away from the car tyres
• Friction is a force caused by two things moving over each over. Rough surfaces produce more friction than small surfaces.
• Friction can be helpful, because it stops us falling when we walk. and brakes that slow down cars or bicycles could not work without friction.
• Friction is not always usefull. It can cause heat and sound and wear away things that rub against each other.
• Oil can reduce the amount of friction. Oil stops the surface touching each other. Liquids that reduce friction are called lubrication.
• Every force has an opposite force working against each other. We call these forces interaction pairs.
• A skydiver is falling from an aeroplane. Identify the two forces which are acting on her.

  The gravitational force, or weight, acts downwards and air resistance acts upwards.
• When forces act on objects they can have the following effects:

  • The object can speed up or slow down. Think about a race car travelling in a straight line whilst it speeds up and slows down.
  • The object can change direction. Think about a satellite orbiting Earth – the gravitational attraction between the satellite and Earth causes the circular motion.
  • The shape of the object can change. Think about squeezing a foam ball.
• When a car turns around a corner, what force is causing the change of direction?

  The change in direction is caused by friction between the tyres and the road.
• A force meter, also known as a newton meter, can be used to measure the size of a force.
• Force meters have a spring inside them. The weight of the mass causes the spring to stretch.
• It is important to ‘zero’ the force meter before you use it. This means adjusting it so that the reading is zero when there is no force acting on it.

  If you don’t ‘zero’ the force meter, all your measurements will be inaccurate by the same amount. This is called a systematic error.
• A force can be described as a push or pull