- When 2 objects interact, they always exert equal and opposite forces on eachother.
- Force is measured in Newtons using a Newtonmeter.
Context: when a car moves forward:
- the force of friction on the ground on the tyre is in the forward direction
- The force of friction on the ground is in the reverse direction
The resultant force is a single force that has the same effect as all the forces acting on the object.
When the resultant force on an object is zero, the object:
- remains stationary
- continues to move at the same speed and in the same direction as it was already moving
On The Road
For any car travelling at constant velocity the resultant force is on zero.
The braking force needed to stop a vehicle depends on:
- the velocity of the vehicle when the brakes are first applied
- The mass of the vehicle
- The greater the velocity, the greater the deceleration needed to stop it in a certain distance.
- The greater the mass, the greater the braking force needed for a give deceleration.
Thinking distance = the distance travelled by a vehicle in the time it takes the driver to react
Braking Distance= the distance travelled by vehicle during the time the braking force acts
The stopping distance = thinking distance + braking distance
Factors Affecting Stopping Distances:
- tiredness, alcohol and drugs all increase reaction times and thinking distance
- The faster the vehicle is travelling, the further it travels before it stops
- In adverse road conditions (e.g-ice) drivers break with less force to avoid skidding. Stopping distances are therefore greater in poor road conditions.