Forces and motion

• Friction

  • Force between an object and the ground that makes it difficult to move
  • Can be reduced using rollers or wheels
• Sleds

  • Used in snowy countries to move heavy loads
• Forwards force on a moving sled is the same size as the force of friction


  Sled will continue to move at a constant speed
• Forwards force on a sled is greater than the force of friction

  Sled will accelerate (get faster)
• Unbalanced forces

  Can change the speed, direction, and shape of something moving
• Changing the shape of a horseshoe

  • Using a force from a hammer
• Forces acting on a moving boat

  • Upthrust
  • Force from wind pushing on sails
  • Water resistance
  • Weight
• Speed

  How far you can travel in a certain time
• Many moving objects do not travel at a constant speed
• Calculating mean speed

  Total distance / Total time
• Converting speed from km/h to m/s

  Divide by 1000, then multiply by 3600
• Distance-time graph

  • Steep line = moving quickly
  • Shallow line = moving slowly
  • Horizontal line = not moving
• Moment

  Turning effect of a force, depends on size of force and distance from pivot
• Effort moment = Load moment

  Lever will not move
• Effort moment > Load moment

  Load will move in the direction shown
• Bottle opener

  • Force multiplier
• Arm

  • Distance multiplier
• Load

  Force being acted upon
• Effort

  Force being applied
• Rope holding barrel moved closer to pivot


  Anticlockwise moment will be smaller
• Calculating new anticlockwise moment

  Force x Distance
• Water resistance and air resistance are forma of drag. Drag forces act to slow down objects moving through fluids. The size of the drag force increases because more of the fluid has to be pushed out of the way each second
• top speed depends on the maximum force that can move it forwards and on the friction/drag slowing it down.
• Falling objects also reach a maximum speed. As the object starts to fall there is no air resistance because it is not moving. As is accelerates the air resistance increases until it balances the weight of the object. The speed at which this happens is called terminal velocity.
• Energy stored in raised objects is called GPE
• Elastic potential energy can be stored in a wound up spring
• Thermal energy is stored in the movement of particles. There is more of this energy in things that are hot. Energy is transferred from hot objects to cooler objects by heating
• Wasted energy is usually transferred to the surroundings by heating and often by sound aswell. This energy is dissipated (spread out). greater effiency less energy is wasted.
• In a distance time graph the gradient of a line represents the speed.
• In a speed time graph the horizontal lines show where she is travelling at a constant speed. The sloping lines show where she is changing speed
• You can move heavy objects with a lever. The lever acts as a force multiplier if the effort distance is greater than the load distance.
• Machines help us to use a smaller force to move an object. Levers and ramps are simple machines. It needs less force to push an object up a slope than to lift it directly.
• Velocity-time graph


  The gradient of the line reveals the acceleration
• Distance-time graph


  The gradient of the line reveals the speed of the object
• Velocity-time graph


  The area under the line is distance travelled
• Resultant force


  The overall value of multiple forces acting on an object
• Resultant forces


  Make objects change in speed in the direction of the force
• Moment


  A turning effect
• Calculating moment


  Moment = Force x perpendicular distance from pivot
• When forces are balanced, there is no change in speed (objects stay still or continue to move at a constant speed)