Braking Force (Oxford AQA IGCSE Physics)

Braking Force

• When a vehicle travels at a steady speed in a straight line (constant velocity), the resistive forces and the driving forces are balanced

• There is no resultant force acting on the vehicle

• So there is no change to the object's motion

• The vehicle continues to travel at a constant velocity in accordance with Newton's first law of motion

Balanced forces acting on a car

• When a driver applies the brakes, there is a frictional force between the brakes and the wheels of the car, also known as the braking force

• This frictional force does work on the brakes - i.e. it transfers energy from the car to the brakes

• Therefore, the kinetic energy of the car decreases and the thermal energy of the brakes increases - i.e. the brakes heat up

• This means the car decelerates (slows down)

Work done when the braking force is applied

• The greater the speed of a vehicle, the greater the braking force required to bring the vehicle to a halt for a given distance

  • This is due to the link between resultant force and acceleration as stated in Newton's second law of motion

  • Since the braking force would need to be larger, the deceleration of the vehicle will be large as well

• Large decelerations could lead to the brake pads overheating and cause the brake discs to warp