Topic 1 - Motion and Forces Flashcards
What is a scalar quantity?
A physical quantities that had magnitude (size), but no direction
What is a vector quantity?
A physical quantity that has both magnitude (size) and direction
What are some examples of a scalar quantity?
- Distance
- Mass
- Speed
- Time
- Energy
- Power
What are some examples of a vector quantity?
- Weight
- Displacement
- Velocity
- Force
- Current
- Acceleration
- Momentum
- Pressure
What happens to the velocity of an object moving around in a circle at constant speed?
Its velocity is continuously changing, as the direction is always changing, e.g., a car going around a roundabout
What is the speed of a person walking?
1.5m/s
What is the speed of a person running?
3m/s
What is the speed of a person cycling?
6m/s
What is the speed of wind speed?
5-20m/s
What is the speed of a car in a built up area?
13m/s
What is the speed of a car on the motorway?
30m/s
What is the speed of a train?
55m/s
What is the speed of a plane?
250m/s
What is the speed of a ferry?
15m/s
What is the speed of sound in air?
340m/s
How do you calculate speed?
speed = distance ÷ time
How do you calculate the distance travelled?
distance = speed * time
What is the symbol equation to calculate the distance travelled?
x = v * t
What is distance measured in?
m (metres)
What is time measured in?
s (seconds)
What is speed measured in?
m/s (metres per second)
What is acceleration?
How quickly velocity is changing, e.g., speed or direction
How do you calculate the acceleration?
acceleration = change in velocity ÷ time
What is the symbol equation to calculate acceleration?
a = (v - u) ÷ t
What is acceleration measured in?
m/s^2
How do you calculate the change in velocity?
final velocity (v) - initial velocity (u)
What is the acceleration for objects in free fall?
10m/s^2
How do you calculate uniform acceleration (constant acceleration)?
v^2 - u^2 = 2 * a * x
What is free fall?
When you assume that gravity only acts on the object, and no extra force is being applied on the object
What are the forces acting on a plane?
- Drag (backwards)
- Lift (upwards)
- Thrust (forwards)
- Weight (downwards)
What are the forces acting on a submarine?
- Water resistance (backwards)
- Buoyancy force (upwards)
- Engine force (forwards)
- Weight (downwards)
What is a distance/time graph used for?
A way of describing the motion of something moving in a straight line
What are the things to remember when interpreting a distance/time graph?
- Gradient = speed
- Straight uphill sections mean it is travelling at a steady speed
- The steeper the graph, the faster it is going
- Flat sections are where it is stationary - it has stopped
- Curves represent acceleration
- A steepening curve means it’s accelerating/speeding up - the gradient is increasing
- A levelling off curve means its decelerating/slowing down - the gradient is decreasing
What is a velocity/time graph used for?
To show an object’s motion
What are the things to remember when interpreting a velocity/time graph?
- The gradient of a velocity/time graph gives the object acceleration.
- Flat sections represent steady speed.
- The steeper the graph, the greater the acceleration or deceleration.
- Uphill sections show acceleration.
- Downhill sections show deceleration.
- A curve means changing acceleration.
How can you find the distance travelled on a velocity/time graph?
The area beneath a velocity/time graph gives the distance travelled.
The distance travelled in any time interval is equal to the
area under the velocity/time graph in that interval.
What is Newton’s first law?
Newton’s First Law says that a resultant force is needed to change the motion
of an object so, a force is needed to make something move, or to
change the speed it’s moving at or the direction it’s moving in.
What happens when there is zero resultant force on a non-moving object?
The object is stationary
What happens when there is zero resultant force on a moving object?
It continues to move at the same velocity, which means all the forces are balanced
What happens if there is a resultant force acting on an object?
The velocity increases
What is Newton’s second law?
The larger the force acting on an object, the more the object accelerates the force and the acceleration are directly proportional.
Acceleration is also inversely proportional to the mass of the object - so an object with a larger mass will accelerate less than one with a smaller mass (for a fixed resultant force).
What is the formula for Newton’s second law?
Force - mass * acceleration
What is the symbol equation for Newton’s second law?
F = m * a
What is force measured in?
N (newtons)
What is mass measured in?
Kg (kilograms)
What is the centripetal force?
A force acting on an object moving in a circular motion directed towards the axis of rotation
What is inertia?
The likelihood of an object moving at the same velocity when no force is being applied.
What does inertial mass measure?
How difficult it is to change the velocity of an object. e.g., if a bowling ball and golf ball came rolling towards you, it would require a larger force to stop the bowling ball than the golf ball
What is the formula to find the inertial mass?
Inertial mass = force ÷ acceleration
What is the symbol equation for the inertial mass?
m = F ÷ a
What is weight?
Weight is the force acting on an object due to gravity (the gravitational force on the object). This force is caused by gravitational fields, and the size of the force depends on the object’s mass and the strength of the gravitational field that the object is in.
What is mass?
The amount of ‘stuff’ in an object. This has the same value, anywhere in the universe.
How do you calculate weight?
weight = mass * gravitational field strength
What is the symbol equation to calculate mass?
w = m * g
What do you measure gravitational field strength in?
N/kg
What is Newton’s third law?
When two objects interact, they exert equal but opposite forces of the same type on each other.
What is a normal contact force?
A pair of forces acting on two touching objects
What is equilibrium?
Objects that are experiencing zero resultant force
What is momentum?
Momentum is a property of moving objects. The greater the mass of an object and the greater its velocity, the more momentum the object has.
How do you calculate momentum?
Momentum = mass * velocity
What is the symbol equation to calculate momentum?
p = m * v
What do you measure momentum in?
kg m/s
What is conservation of momentum?
The total momentum before an event (e.g. a collision or an explosion) is the same as after the event, in a closed system
What happens to the momentum when a non-zero force acts on a moving object?
It causes the velocity to change, which means the momentum also changes
How do you calculate the force and change of momentum?
Force = change in momentum ÷ time
What is the symbol equation to calculate the force and change of momentum?
F = (mv - mu) ÷ t
What does a larger force mean, in terms of momentum?
There is a faster change in momentum
What is Hooke’s law?
Spring force = spring constant * extension
What is the symbol equation for Hooke’s law?
F = k * x
What is the stopping distance of a vehicle?
The distance covered in the time between the driver first spotting a hazard and the vehicle coming to a complete stop.
How do you calculate the stopping distance of a vehicle?
Stopping distnace = thinking distance + braking distance
How do you calculate the energy transferred in stretching a spring?
Energy transferred in stretching = 1/2 * spring constant * (extension^2)
What is the symbol equation to calculate the energy transferred in stretching a spring?
E = 1/2 * k * x^2
What is energy transferred in stretching measured in?
J (joules)
What is extension measured in?
m^2
What is spring constant measured in?
N/m (newtons per metre)
What is the thinking distance?
The thinking distance is the distance the vehicle travels during the driver’s reaction time (the time between seeing a hazard and applying the brakes).
What is the braking distance?
The braking distance is the distance the vehicle travels after the brakes are applied until it comes to a complete stop, as a result of the braking force.
What is thinking distance affected by?
- The speed of the vehicle - whatever your reaction time, the faster you’re going, the further you’ll go in that time.
- How quick to respond you are, i.e. your reaction time this can be affected by tiredness, drugs, alcohol and distractions.
What is braking distance affected by?
- The faster you’re going, the further it takes to stop.
- The mass of the vehicle -vehicles with a larger mass (e.g. lorries, cars full of passengers) will take longer to stop.
- How good your brakes are - all brakes must be checked and maintained regularly. Worn or faulty brakes won’t be able to apply as much force as well-maintained brakes and could let you down catastrophically just when you need them the most, i.e. in an emergency.
- The amount of friction between the vehicle’s tyres and the road surface. The less friction there is between the tyres and the road, the more likely the vehicle is to skid, which increases stopping distance.
The amount of friction is affected by:
1) How good the tyres are tyres should have a minimum tread depth of 1.6 mm. In wet conditions, the tread pattern helps to stop water getting trapped between the tyres and the road - they provide a channel through which the water can ‘escape’. With too little tread, the tyres may lose contact with the ground, causing the vehicle to slide.
2) The state of the road-water, ice, leaves, diesel spills, muck on the road etc. can result in reduced friction between the tyres and the road and so can greatly increase the braking distance.
What is the braking distance equation?
1/2 * mass * (speed^2) = force * braking distance
What is the symbol equation for breaking distance?
1/2 * m * v^2 = F * d
