forces

• Force


  A push or pull
• What a force can change

  • Shape
  • Speed
  • Direction of movement
• Types of forces


  • Non-contact forces
  • Contact forces
• Non-contact forces


  • Gravitational force
  • Magnetic force
  • Electrostatic force
• Contact forces


  • Air resistance
  • Water resistance
  • Frictional force
  • Upthrust
  • Elastic force
• Contact forces


  Force needs to touch the object before it gets affected by the force applied
• Non-contact forces


  Force which acts on an object without coming physically in contact with it
• Weight


  The gravitational force pulling on objects
• Mass


  Amount of matter that makes up an object (grams [g], kilograms [kg])
• On Earth, mass can be 210 kg and weight would be 2100 N
• On the Moon, mass can be 210 kg and weight would be 344 N
• The force of gravity is greater on Earth than on the Moon


  Because the Earth's gravity pulls on every kilogram with a force of 10 N
• For something that has a mass of 2 kg, it has a weight of 20 N
• Mass of 40 kg has a weight of 400 N
• 1 kg = 9.8 N (gravitational field strength)
• Hooke's Law


  The extension is proportional to the force
• Springs


  • Materials and objects can be stretched or compressed
  • The amount of stretch or compression depends on the type of material and size of force
  • An extension of a spring = the difference between original and stretched length
  • A spring is elastic because it will return to its original length when the force is removed
• Limit of proportionality


  Hooke's law - the extension is proportional to the force up to a certain point
• For every 1 N increase in the force, the spring stretches by the same amount
• Gravitational force

  Pulling force by the Earth's gravity
• The greater the gravitational force acting on an object, the heavier the object is
• Friction


  Force between two touching objects
• Effects of friction

  • Slows things down
  • Makes things stay still
• Friction can be increased by using rubber which produces a lot of friction
• Friction can wear and tear things away
• Bicycle is hard to ride if there is too much friction between the axles
• Air resistance


  A force that slows down falling or moving objects
• Air resistance pulls you up
• Pressure


  The amount of force exerted on a certain area
• The pressure is higher when the area in contact is smaller, or if the force applied is larger
• Sharp objects exert high pressures on surfaces, using sharp objects less force is required to create a high pressure
• The deeper you dive in, the higher the water pressure
• Larger force → higher pressure, Smaller force → lower pressure
• Balanced forces


  Two forces acting on an object that are the same size, so nothing will change
• Unbalanced forces


  Two forces acting on an object where one is stronger than the other, so it will start to move
• If unbalanced forces are acting on a moving object, it will change speed
• All stationary objects have balanced forces acting on them
• If the forces are balanced, the object moves on with the same speed
• If the forces are unbalanced, the object will change speed