Speed – how fast you’re going
Velocity – how fast you’re going in what direction.
Distance in a particular direction is called displacement.
Average velocity = displacement / time
Speed cameras use the lines painted on the ground to see how fast a car is going in a certain number of seconds.
Acceleration = change in velocity / time taken
• Stationary object – all forces in balance
• Steady velocity – all forces in balance
• Acceleration – unbalanced forces
Balanced force – steady speed and direction
Resultant force – acceleration
Resultant force = mass x acceleration
Reaction forces – if an object exerts a force on another object, that object will exert the exact opposite force
Friction and Drag
Always there, slows things down, always in the opposite direction to movement.
Steady speed = driving force needs to balance the friction
Reduce drag – use streamlining
Drag increases as speed increases
When resistance force = accelerating force – cannot go any faster
Thinking distance – speed and attention
Breaking distance – speed, weight, brakes and grip
Momentum = Mass x velocity
The longer the change in momentum the smaller the force once it reaches impact, so cars have:
1) Crumple zones – increase the time taken for the car to stop.
2) Seat belts – stretch slightly increasing the time taken for the wearer to stop, reduces forces acting on the chest.
3) Air bags – slightly increasing the time taken for the driver to reach impact.
Kinetic energy = ½ x Mass x Velocity2
Work done = Force x Distance
Electrical energy = voltage x current x time
Gravitational Potential energy
Potential energy = mass x g (normally 10) x height
Conservation of energy
Energy is never created or destroyed – only converted from one form to another.
Energy is only useful when it’s converted from one form to another.
Kinetic energy gained = potential energy lost
Speed of falling object = potential energy is converted into kinetic energy.
Power – watts or J/s
Power = work done / time taken
Power output = energy transferred (potential or kinetic energy) / time taken
Velocity is both the speed and direction of an object so when going in a circle the velocity is always changing so this means there must be a force acting on it = centripetal force.
Centripetal Force (N) = (Mass x Speed2) / Radius
Used thought experiments – fancy way of…