2) Motion and Forces Flashcards
What is distance?
Scalar quantity
How far an object moves
What is displacement
Vector quantity
The distance an objecty moves in a straight line from start to finish
What is speed?
Scalar quantity
No direction
What is velocity?
Vector quantity
Direction as well as speed
How do you add vectors?
Draw each vector as an arrow
Legnth represents magnitude
Direction represents direction
Work out the resultant force of 10N by a force and 10N at a right angle to that force?
Pythagoras
root(100 + 100) = root (200) = 14.1N
What does a distance time graph’s gradient show?
An object’s distance
How is a distance time graph’s gradient altered by speed?
Slower speed = less steep
Quicker speed = more steep
What is on the axis of a distance time graph?
Y axis- distance
X axis time
What is on the axis of a speed time (velocity time) graph?
Y axis- speed
X axis- time
What does a horizontal line mean on a speed time graph?
The object is moving at a constant speed
What do curved lines show on a speed time graph?
An object is accelerating or decelerating at a rate that is not constant
What do straight lines show on a speed time graph?
An object’s acceleration is constant
What is the area under a speed time graph equal to?
The distance travelled by an object
What can acceleration be?
A change in speed
A change in direction
A change in speed and direction
What is the resulant force?
The sum of all forces acting on an object
What does having unbalanced forces acting on an object mean?
A resultant force is acting on the object
What is the equation for resultant force?
resultant force = mass x acceleration
F = m x a
What is Newton’s 1st law?
The velocity of an object will only change if a resultant force is acting on the object
How does no resultant force affect a moving object?
It will continue to move in the same direction and speed (velocity)
What is Newton’s 3rd law?
When two objects interact, the forces they exert on each other are equal and opposite
How is average speed calculated?
total distance / total time
How can we measure average speed?
Light gates
How is speed calcualated through light gates?
speed = length of card / time taken to pass through gate v = x / t
What is average speed usually measured in?
Metres per second
m/s
How is acceleration calculated?
average velocity / time
What is the equation for final speed?
final speed = intial speed + (acceleration x time)
v = u + a x t
What is the equation for distance?
distance = intial velocity x time + 0.5 x acceleration x time^2
How is momentum of an object calculated?
mass x velocity
p = m x v
How is change in momentum calculated?
momentum = force x time
p = f x t
momentum = mass x final velocity - mass x inital velocity
mv - mu
What is the law of conservation of momentum?
Momentum cannot be created or destroyed
If two objects collide sum of momentum before collision = sum of momentum after collision
What safety features do cars have?
Seat belts
Air bags
Crumple zones
How do car safety features reduce injuries?
Absorb energy
Increase time taken for change in momentum to happen, reducing involved forces
What is the unit for momentum?
kgm/s
What is the mass of an object?
The measure of the matter it contains
What does mass being constant mean?
It is the same on earth, moon, sun
What is inertia?
How difficult it is to change an object’s motion
How does mass affect inertia?
Higher mass = more inertia
What is the equation for weight?
weight = mass x gravitational field strength
What is weight measured in?
Newtons
What is weight defined as?
The force acting downwards on an object due to gravity
What is the constant rate at which objects in free fall fall called?
Acceleration due to gravity (g)
What is Earth’s gravitational field strength?
9.81 m/s^2 (10m/s^2)
Why don’t objects continue to accelerate indefinitely?
Air resistance slows them down
What type of force is air resistance?
A frictional force
How does air resistance change as the speed of a falling object increases?
Falling quicker = more air resistance
What is centripetal force?
The resultant force that acts towards the middle of a circle
What is stopping distance?
The distance it takes a car to stop in an emergency
What is the calculation for stopping distance?
Stopping distance = thinking distance + breaking distance
What is thinking distance?
The time it takes for a driver to react to a situation and break
What is breaking distance?
The distance the car travels between breaks applied and car stopping
What factors affect thinking distance?
Tiredness
Drugs
Alchohol
Distractions
What factors affect breaking distance?
Condition of car
Initial car speed
Road conditions
What is the reaction time test?
Ruler drop test
What is the typical reaction time for a human?
0.25 s
What equations can be used to measure reaction time?
v^2 - u^2 = 2as
a = (v-u) / t
What is the symbol for initial velocity in physics?
u
What is the symbol for final velocity in physics?
v
What is the symbol for acceleration?
a
What is the typical speed for a motorway car?
30 m/s
What does braking cause?
Friction
What is the enrgy change of breaking a car?
Kinetic in wheels –> thermal in brakes
What factors require a greater braking force?
Higher speed
Higher mass
When a car comes to a stop what must the work done by the brakes be equal to?
Work done = initial kinetic energy
What is the equation for work done with braking?
F x d = 0.5 x m x v^2
Work done = half x mass x velocity squared
What are dangers of large decelerations?
Brakes can overheat
Car can skid
How can theforce in an emergency stop be calculated?
change in momentum / time taken
What is the equation for force?
force = change in momentum / time taken
What does a vector quantity have?
Direction
Magnitude
What does a scalar quantity have?
Magnitude
