P2.1 Forces and their effects Flashcards
What happens when two objects interact?
The forces they exert on each other are equal and opposite
What may a number of forces acting at a point be replaced by?
A single force that has the same affect on the motion as the original forces all acting together, this single force is called the resultant force
What may a resultant force acting on an object cause?
A change in its state of rest or motion
What happens if the resultant force acting on a stationary object is zero?
The object will remain stationary
What happens if the resultant force acting on a stationary object is not zero?
The object will accelerate in the direction of the resultant force
What happens if the resultant force acting on a moving object is zero?
The object will continue to move at the same speed and in the same direction
What happens if the resultant force acting on a moving object is not zero?
The object will accelerate in the direction of the resultant force
What is the acceleration of an object determined by?
The resultant force acting on the object and its mass
What is the equation for resultant force and acceleration?
a = F/m or F = m x a
What is the resultant force measured in?
Newtons, N
What is the mass measured in?
Kilograms, Kg
What is acceleration measured in?
Metres per second squared, m/s squared
What does the gradient of a distance-time graph represent?
Speed
How do you calculate speed on a distance-time graph?
vertical axis / horizontal axis (should be distance/time)
What is the velocity of an object?
It’s speed in a given direction
What is the equation for acceleration with velocity?
v - u
a = ——–
t
What is velocity measured in?
m/s
What does the v stand for?
Final velocity
What does the u stand for?
Initial velocity
What does the gradient on a velocity-time graph represent?
Acceleration
How do you work out the acceleration from a velocity-time graph?
Vertical axis / horizontal axis
How do you work out the distance from a velocity-time graph?
Work out the area beneath the line
When a vehicle travels at a steady speed…
The resistive forces balance the driving force
What are most resistive forces caused by?
Air resistance
The greater the speed of a vehicle…
The greater the braking force needed to stop it in a certain distance
The greater the speed of a vehicle…
The greater the stopping distance
What is the stopping distance of a vehicle?
The sum of the distance the vehicle travels during the driver’s reaction time (thinking distance) and the distance it travels under the braking force (braking distance)
What can a driver’s reaction time be affected by?
Tiredness, drugs, alcohol and sometimes distractions
What happens when the brakes of a vehicle are applied?
The work done by the friction force between the brakes and the wheel reduces the kinetic energy of the vehicle and the temperature of the brakes increase
What can a vehicle’s braking distance be affected by?
Adverse road and weather conditions and poor condition of the vehicle
What do adverse road and weather conditions include?
Wet or icy conditions
What does poor condition of the car entail?
Poor condition of the car’s brakes or tyres
The faster an object moves through a fluid…
The greater the frictional force that acts upon it
What will an object travelling through a fluid initially do?
Accelerate due to the force of gravity
What will happen eventually when an object is travelling through a fluid?
The resultant force will be zero and the object will move at its terminal velocity, a steady speed
Why do parachutes reduce terminal velocity?
Because their large surface area increases air resistance
How do you calculate the weight of an object?
W = m x g
What does g stand for?
The gravitational field strength
What is gravitational field strength measured in?
Newtons per kilogram, N/Kg
What is the gravitational field strength on earth?
10N/Kg
What is weight measured in?
Newtons, N
What may a force acting upon an object cause?
A change of shape of the object
What will a force being applied to an elastic object, such as a spring, result in?
The object stretching and storing elastic potential energy
For an object that is able to recover its original shape, where is elastic potential energy stored?
In the object when work is done on the object to change its shape
What is the extension of a plastic object directly proportional to?
The force applied, provided that the limit of proportionality is not exceeded
What is the equation to work out the force with a spring and extension?
F = k x e
What does k stand for?
The spring constant in newtons per metre, N/m
What does the e stand for?
Extension in metres, m
