(forces and accleration)

• velocity is the speed of something in a given direction
• scalars are properties which only have size (e.g volume)
• vectors are properties that have both size and direction (e.g. weight)
• formula for acceleration is (v-u)/t
• mass is the amount of matter
• deceleration is when an object accelerates backwards. (negative acceleration)
• reaction time - braking distance - stop
• total stopping distance = reaction distance + braking distance
• work done = Fxd
• when moving, a car has kinetic energy, it is transffered to thermal energy when work is done by brakes
• when an object changes shape permanently, it has been deformed
• if object returns to original shape after stretching, it is elastic
• if the object is deformed after applied force, it is plastic
• force is directly proportional to extentsion
• the higher the spring constant, the stiffer the material
• Hooke's law is that within an elastic limit, the extension of an object is directly proportional to the force that causes an extension
• average speed = distance moved/time taken
• distance = speed x time
• speed = distance/time
• time = distance/speed
• in velocity-time graph, acceleration = gradient = rise/run
• in velocity-time graph, distance = area
• formula for constant acceleration is v^2 = u^2 + 2as
• forces can cause objects to

  • change direction
  • change speed
  • change shape
• when a force is exerted on an object, another force will be exterted in the opposite direction
• scalars are quantites that only have magnitude (e.g. mass)
• vectors are quantites that have both magnitude and direction (e.g. velocity)
• friction is the force that opposes motion
• forces can combine to proudce balanced or unbalanced force. Balanced force is when the opposite forces are equal, unbalanced forces is when the opposite forces are unequal
• weight is a force acting on an object due to gravity
• formula for weight is w= mg
• stopping distance = thinking distance + braking distance
• braking distance can be affected by

  • speed of car
  • road conditions
  • brake efficiency
• reaction distance can be affected by

  • road conditions
  • alertness of driver
  • alcohol or drug intake
• falling objects experience weight and air resistance. The force of air resistance increases with speed, eventually large enough to balance the downwards weight force. This means that the resultant force is 0. This is called terminal velocity

  
• when an object has been stretched to its limit of proportionality, it will begin to inelastically deform (limit according to material)