Physics : Motion and Forces Flashcards
What do vectors have?
Magnitude (size) and Direction
What do scalars have?
Magnitude (size) but not Direction
Distance is an example of what quantity?
Distance is a scalar quantity
Speed and velocity both show what?
Both show how fast you are going
Displacement is an example of what quantity?
Displacement is a vector quantity
Acceleration shows what?
It shows how quickly you are speeding up
What does uniform acceleration mean?
It means constant acceleration
Name 3 examples of vector quantities:
Force, velocity, displacement, weight, acceleration and momentum
Name 3 examples of scalar quantities:
Speed, distance, mass, energy, temperature and time
What is displacement?
Displacement measures the distance and direction in a straight line from an object’s starting point to it’s finishing point.
What is the equation that links speed, distance and time?
Distance travelled (m) = average speed (m/s) x time (s)
What is the typical walking speed?
1.4 m/s
What is the typical running speed?
3 m/s
What is the typical cycling speed?
5.5 m/s
What is the typical speed for cars in a built-up area?
13 m/s
What is the typical speed for aeroplanes?
250 m/s
What is the typical speed for cars on a motorway?
31m/s
What is the typical speed for trains?
Up to 55 m/s
What is the typical wind speed?
5-20 m/s
What is the typical speed of sound in air?
340 m/s
What is the typical speed of ferries?
15 m/s
What is the equation that links acceleration, change in velocity and time?
Acceleration = change in velocity / time
What is the equation for constant/uniform acceleration?
v2 - u2 = 2as
What do distance/time graphs show?
They show how far something has travelled
How do you find the speed from a distance/time graph?
The gradient is equal to the speed, so change in y over change in x
What do velocity/time graphs show?
They show acceleration
What does the gradient on a velocity/time graph represent?
The acceleration
What does a flat section represent on a velocity/time graph?
A steady speed
What do the uphill sections (/) on a velocity/time graph represent?
They represent acceleration
What doe the downhill sections () on a velocity/time graph represent?
They represent deceleration
How do you work out the distance travelled on a velocity/time graph?
The area under the curve is the distance
What is needed to change motion?
A force
What is Newton’s First Law?
stationary and moving
If the resultant force on a stationary object is zero, the object will remain stationary. If the resultant force on a moving object is zero, it will carry on moving at the same velocity
What is acceleration directly proportional to?
The resultant force
What is the equation that links force, mass and acceleration?
Force = mass x acceleration
Are weight and mass the same thing?
No
What is weight?
Weight is the force acting on a object due to gravity
Is weight a vector or scalar quantity?
Weight is a vector
What is the equation that links weight, mass and gravity?
Weight (N) = mass (kg) x gravity (N/kg)
What is centripetal force?
A force that keeps something moving in a circle
What is inertia?
The tendency to keep moving with the same velocity
What does an objects’ inertia mass measure?
It measures how difficult it is to change the velocity of an object
How can you calculate the inertia mass?
Use Newton’s Second Law :
m = F/a
What is Newton’s Third Law?
When two objects interact, the forces they exert on each other are equal and opposite.
What is momentum?
It is the product of the object’s mass and velocity
How do you calculate momentum?
momentum (kg m/s) =
mass (kg) x velocity (m/s)
p = m x v
Is momentum a vector or scalar quantity?
It is a vector quantity - it has size and direction
What happens to the momentum when the mass or velocity of an object increases?
The momentum also increases
What happens to the total momentum before and after an event in a closed system?
The total momentum before and after an event stays the same
What is it called when the total momentum before and after an event stays the same?
Conservation of momentum
What can force do to momentum?
Force can cause changes in momentum
What happens when a resultant force acts on an object?
It causes a change in momentum
What is the equation that links force, change in momentum and time?
Force (N) = change in momentum (kg m/s) / time (s)
F = (mv-mu)/t
If the change in momentum gets faster, what happens to the force?
The force gets bigger
What is the thinking distance?
The distance the car travels in the driver’s reaction time
What is stopping distance?
It is the thinking distance + the braking distance
What affects the thinking distance?
Reaction time - distance is increased by tiredness, alcohol, drugs and distractions
Speed - faster you’re going the further you will travel during your reaction time
What is the braking distance?
The distance taken to stop once the brakes have been applied
What affects the stopping distance?
Speed - the faster you’re going the longer it takes to stop
Mass of car - car full of people won’t stop as quickly as an empty one
Condition of brakes - worn or faulty ones won’t brake with as much force
Friction between tyres and road - if the tyre tread is worn or there is dirty/icy/wet conditions then you are likely to skid
What is the equation that measures the energy transfer from the car to it’s brakes?
Energy in car’s kinetic energy store = work done by brakes
0.5 x m x v^2 = F x d
