Laws of motion (pg 6-11)

• First Newton Law - Balanced forces mean no change in velocity
• So long as the forces on an object are all balanced, then it'll stay still, or else it it's already moving it'll just carry on at the same velocity - so long as the forces are all balanced
• When an object is moving at a constant velocity then the forces on it must all be balanced
• To keep things at a steady speed, there must be zero resultant force
• Second Newton Law - A resultant force means acceleration
• If there is an unbalanced force, then the object will accelerate in that direction
• The overall unbalanced force is called the resultant force
• Acceleration can take five different forms:

  • Starting
  • Stopping
  • Speeding up
  • Slowing down
  • Changing direction
• Resultant force = Mass * Acceleration
• Force = Mass * Acceleration
• Formula for resultant force: $F=$$ma$
• Third Newton Law - Reaction forces. If object A exerts a force on object B then object B exerts an equal and opposite force on object A
• Vectors have size and direction - scalar quantities only have size
• Vector quantities: force, velocity, acceleration, momentum, etc.
• Scalar quantities: mass, temperature, time, length, etc.
• To work out the resultant force you need to combine vectors
• Moving objects can reach a terminal velocity
• Frictional forces increase with speed, but only up to a certain point
• When an object first starts to fall, it has much more force accelerating it than resistance slowing it down. As its velocity increases, the resistance builds up. This resistance force gradually reduces the acceleration until the resistance force is equal to the accelerating force. The object has reached its terminal velocity
• The terminal velocity of falling objects depends on their shape and area
• The accelerating force acting on all falling objects is gravity and it would make them all accelerate at the same rate, if it wasn't for air resistance
• The drag depends on its shape and area
• Air resistance causes things to fall at different speeds, and the terminal velocity of any object is determined by its drag compared to its weight
• Terminal velocity is when resistance equals weight
• Hooke's Law says that extension is directly proportional to force
• Hooke's Law stops working when the force is great enough
• If you increase the force on a wire past its elastic limit, the material will be permanently stretched
• Some materials, like rubber, only obey Hooke's Law for really small extensions
• Elastic behaviour - when a material returns to its original shape once the forces are removed
• Metals display elastic behaviour as long as Hooke's Law is obeyed
• Stopping Distance = Thinking Distance + Braking Distance
• Thinking distance - the distance the car travels in the time between the driver noticing the hazard and applying the brakes
• Thinking distance is affected by two main factors:

  • How fast you’re going
  • Your reaction time
• Reaction time is affected by things like tiredness, drugs, alcohol and old age. Inexperience can also affect this
• Braking distance - the distance the car travels during its deceleration whilst the brakes are being applied
• Braking distance is affected by four main factors:

  • How fast you’re going
  • The mass of the vehicle
  • How good your brakes are
  • How good the grip is
• The grip depends on 3 things:

  1. Road surface
  2. Weather conditions
  3. Tyres