P2.2 Flashcards
What can a force do?
It can change the shape of an object or change its state of rest or its motion.
What happens when two objects push or pull on each other?
They exert equal and opposite forces on one another.
What happens to the forces to pull a tractor out of the mud?
The force of the ground on the tractor needs to be greater than the force of the mud on the car.
What is the motive force?
Driving force on a farthest makes it move.
What causes the motive force?
The friction between the ground and the tyres.
Where does friction occur?
Where the two objects are in contact.
What happens when the resultant force is zero?
- remains stationary
- continues to move at a constant speed in the same direction
What is a resultant force?
A single force.
What happens when the resultant force is not zero?
The movement of the car depends on the size and direction of the resultant force.
What happens to the resultant force if an object is acted on by two unequal forces acting in opposite directions?
- it’ll be equal to the difference between the two forces
- it’ll be in the direction of the larger force
What is the equation for resultant force?
=mass (kg) X acceleration (m/s2)
What are forces measured in?
Newtons.
What happens if a velocity increases?
The resultant force is in the same direction as the velocity.
What happens if the velocity decreases?
The resultant force is opposite in direction to its velocity .
What happens if the driver presses harder on the accelerator?
It varies the driving force of the engine.
What does the braking force needed to stop a vehicle in a certain distance depend on?
- the speed of the vehicle when brakes are applied
- the mass of the vehicle
What is the stopping distance affected by?
Braking and thinking distance.
What is the equation for the stopping distance?
= thinking distance + braking distance
What is the thinking distance?
Distance travelled by the vehicle in the time it takes the driver to react.
What is the braking distance?
Distance travelled by the vehicles once the brakes have been applied.
What affects the stopping distance?
- tiredness,alcohol,drugs
- speed vehicle is travelling at
- road conditions
- poorly maintained vehicles
What is the weight of an object?
Force of gravity on it.
What is the mass of an object?
Quantity of matter in it.
What is the equation for weight?
=mass (kg) X gravitational field strength (N/kg)
What is the resultant force if an object falls with no other forces acting on it?
The resultant force on it is its weight.
What happens if an object falls in a fluid?
The fluid drags on the object.
What is terminal velocity?
When an object reaches a constant speed and the drag force is equal and opposite to its weight.
What is air resistance?
Drag force when an object is moving through air.
What happens to an elastic object when the forces deforming it are removed?
It regains its original shape.
What is the extension?
The increase of length from its original shape.
What is the equation for the extension?
=extension - original length
What happens when an elastic object is stretched?
The elastic potential energy is stored in the object.
What happens when the stretching force is removed?
The elastic energy stored in the object is released.
Why does an object stretch more than predicted?
It has been stretched beyond its limit of proportionality.
What is Hooke’s law?
The extension is directly proportional to the force applied to it, provided its limit of proportionality is not exceeded.
What is the equation to Hooke’s law?
force applied(N)=Spring constant(N/m) X extension(m)
What is the spring constant equal to?
The force per unit extension needed to extend the spring.
Why does reducing the speed reduce the fuel it uses?
Because air resistance at high speed is greater than at low speed so more fuel is used.
How can drivers reduce their fuel usage? How?
By fitting a wind deflector over the cab.
Reduces the air resistance.
Name 2 ways that have reduced speeding:
- speed cameras
- anti-skid surfaces
