Forces Y2

• Force


  A push or pull
• A force cannot be seen but the effects of a force can be seen or felt
• SI unit for force

  Newtons (N)
• Balanced forces


  Two forces acting on an object are equal in size but act in opposite directions (object is stationary/moving at a constant speed)
• Unbalanced forces


  Two forces acting on an object are not equal in size (objects moving but not at a constant speed)
• Resultant force


  The overall force acting on an object
• If the resultant force is 0N, the object is either stationary or moving at a constant speed
• If the resultant force is greater than 0N, the object is moving but not at a constant speed
• Net force


  When the forces are balanced, there is no net force so the object can be stationary or moving with the same speed
• Net force


  When the forces are unbalanced, there is a net force so the object will start moving or move with the changing speed
• Types of forces


  • Contact forces
  • Non-contact forces
• Contact forces


  Forces that act when objects touch/When an object is touched, contact forces act on it
• Non-contact forces


  Forces that act at a distance from an object
• Frictional force


  Opposes motion, exists between the surfaces of two objects which are in contact with each other
• Normal force


  The force that a surface exerts on an object, force that surfaces exert to prevent solid objects from passing through each other, always perpendicular to the surface exerting the force/the surfaces in contact
• Gravitational force


  Pulls objects to the centre of planets like Earth, pulls radially inwards, exists between any two objects with mass, force that attracts two objects towards each other, affected by distance (further away, feel less gravitational force)
• Electrostatic force

  Push or pull between electric charges
• Magnetic force


  Push or pull between magnets or a magnet and a magnetic object
• Effects of forces


  • Changes the shape of an object
  • Changes the size of an object
  • Causes a stationary object to move
  • Stops a moving object
  • Causes a moving object to change speed
  • Causes a moving object to change direction
• Effects of friction


  Slows down and stops a moving object, heat (and sound) is produced in the process
• Ways to reduce friction

  • Using smooth surfaces (eg lane of bowling alley)
  • Using ball bearings (eg to make moving parts of machinery move faster/reduce wear and tear)
  • Applying lubricants (eg oiling parts of a bicycle)
  • Using streamlined shapes which reduces air resistance (friction) (eg streamlined shape of an aeroplane)
  • Using a layer of air to move about easily which reduces contact (eg maglev trains hover over the tracks to reduce frictional force between the base of the train and the tracks)
• Turning effect of a force

  As the Force increases, the turning effect increases. As the perpendicular distance of the force from the pivot increases, the turning effect increases.
• Levers


  A lever is a device that turns when a force is exerted. Pivot = The point at which the lever turns. For the same turning effect, as force increases, distance of force from pivot decreases.
• Weight


  It is a measure of the force of gravity exerted on an object. When a planet exerts a gravitational force on an object and pulls it towards its centre, the object has weight. When weight increases, the amount of gravitational force also increases. Measured using a spring balance. SI units : Newtons (N)
• Mass


  Amount of matter in an object, constant regardless of location, SI Unit - kilogram (kg), measured by beam balance, electronic balance
• Weight


  Gravitational force acting on an object, may vary according to location, SI Unit - Newton (N), measured by spring balance
• Pressure


  Pressure is the force acting perpendicularly per unit area. Pressure = Force/Area. The SI unit for Pressure is Pascal (Pa). 1 Pa = N/m^2. Can be increased by increasing the force or reducing the area. Can be decreased by decreasing the force or increasing the area.
• Atmospheric pressure


  The air presses on us in all directions. As height increases (go higher, eg when up a mountain), pressure decreases.
• When drawing forces, for contact forces, draw the arrow from the point of the contact/where the force is exerted. If there are many contact points, draw from the middle of the contact points.
• To draw gravitational force, we have to draw the arrow from the centre of gravity (the middle of the object).
• To draw the normal force, always start from the surface (point of contact)
• The arrows drawn (their length and width) have to be reflective of the direction and magnitude of the force.
• Say "force of the same magnitude" instead of "same amount of force"
• Turning effect = force x perpendicular distance