What is newtons second law?
The acceleration of an object is:
- directly proportional to the resultant force of an object
- inversely proportional to the mass of an object
What is the equation for force?
Force = mass x acceleration
What is inertia?
The tendency for an object to stay at rest or to continue in uniform motion (constant velocity) is called inertia
What is inertial mass?
Inertial mass refers to the measure of difficulty in changing an object velocity
What is weight?
The weight of an object is the force acting on it due to gravity. Weight is measured in newtons.
Weight can be calculated by multiplying the mass by the gravitational field strength
What is mass?
The mass of an object depends on the quantity of matter in it. Mass is measured in kilograms
What is terminal velocity?
The maximum velocity that and object can travel at in a fluid (liquid and gas)
When does a skydiver first reach terminal velocity before opening his parachute?
When the air resistance becomes big enough to balance the skydivers weight. At this point the forces are balanced so his speed is constant.
When does the skydiver reach terminal velocity after opening his parachute?
As he slows down his air resistance will decrease again until it balances his weight. The skydiver has now reached a new lower terminal velocity
What is the equation for stopping distance?
Total stopping distance = thinking distance + breaking distance
What is thinking distance?
Thinking distance is the distance travelled between the driver realising he needs to break and actually breaking. Or the distance travelled during the reaction time.
What personal factors affect the thinking distance?
- Under the influence (drugs/ alcohol)
- vision/ visibilty
- speed
- concentration (tiredness)
- distractions
What is braking distance?
The braking distance is the distance taken to stop once the brakes are applied
What external factors can affect the breaking distance of a vehicle?
- Weather/conditions of the road
- mass
- speed
- friction
- conditions of the tyres or brake pads
What is momentum?
A property of a moving object which depends on how much mass the object has and how fast it is moving
What is the equation for momentum?
Momentum = mass x velocity
P= mv
What is conservation of momentum?
In a closed system momentum before an event is the same as the momentum after an event
What is a closed system?
A physical system that does not exchange matter or energy with its surroundings
What safety features does a car have?
Crumple zone, seat belt, air bags
What do the safety features do?
They all increase the collision time which decreases the impact on the people inside the vehicle.
The airbag and crumple zone have a large surface area to distribute the collisin force
How to change the momentum of an object?
In order to change the momentum of an object a force must be applied. The magnitude of the force depends on the size of the change in momentum and how long it takes to change the momentum.
What is an elastic object?
An elastic object is one which regains its shape when the forces deforming it (e.g stretching or squashing) are removed. When an elastic object is deformed the energy which caused it to deform is stored as elastic energy which is released when the force is removed.
What is compression?
When a for e is exerted on an object (a spring for example) it will be compressed (push the spring together)
What is tension?
As well as compression an object (spring for example) can be in tension this is when a force pulls on the object (stretching a spring)
