What is Newton’s second law of motion
- The acceleration of an object is PROPORTIONAL to the resultant force acting on the object (if we have a greater force, we have a greater acceleration)
- and INVERSELY PROPORTIONAL to the mass of the object (if the mass is larger then the acceleration will be smaller)
Force needed to accelerate an object equation
Force (n) = mass (kg) x acceleration (m/s squared)
Road transport speed, acceleration and force
- on main road, cars travel at 13 m/s in the UK
- on a motorway 30 m/s
- accelerating from a main road to a motorway is usually 2 m/s squared
- for a typical family car, this would require a force of 2000N
What is the property called when objects will stay still or keep the same motion unless you apply a resultant force
Inertia
What is the inertial mass
- A measure of how difficult it is to change the velocity of an object
- the larger the inertial mass, the greater the force needed to produce a given acceleration
What is Newton’s third law of motion
Whenever two objects interact, the forces they exert on each other are equal and opposite
What is the stopping distance in terms of vehicles
The stopping distance is the total distance travelled from when the driver first spots the obstruction to when the car stops
What is the thinking distance
The distance travelled by the car during the driver reaction time
What is the reaction time
The time taken for the driver to spot the obstruction, make a decision and then move their foot to the brake
What is the braking distance
The distance the car travels from when the driver applies the brakes to when the car stops
What happens to the stopping distance if the speed of the vehicle increases
The greater the speed of the vehicle, the greater the stopping distance (if same braking force is applied)
What factors can make a driver have a longer reaction time
- tiredness
- alcohol
- drugs
- distractions
What happens to the thinking distance if the reaction time is greater
The longer the reaction time, the longer the thinking distance
What factors increase the braking distance
- wet or icy conditions
- worn tires
- worn brakes
- mass in vehicle
What is the overall stopping distance
Thinking distance + braking distance
What happens to the braking force the greater the speed
The greater the speed, the greater the braking force needed to stop the car in a certain distance
What will a large braking force cause
It will cause the car to decelerate rapidly
What would happen if the brakes overheat
The driver could lose control of the vehicle
How to calculate the force needed to decelerate
Force (n) = mass (kg) x acceleration (m/s squared)
Momentum
- All moving objects have momentum
- if an object is not moving, its momentum is zero (no momentum)
Momentum equation
Momentum (kg m/s) = mass (kg) x velocity (m/s)
What happens in a closed system (conservation of momentum)
In a closed system, the total momentum before an event is equal to the total momentum after an event (momentum has been conserved)
