Forces & Motion Flashcards
What are scalars?
Numbers that only have size
What are 3 examples of scalars?
- Time
- Distance
- Speed
How do you calculate speed?
Speed = Distance
—————
Time
What are vectors?
Numbers that have size AND direction
What are some examples of vectors?
- Displacement
- Velocity
- Forces
How do you calculate velocity?
Displacement
———————
Time
Which changes:
Mass or weight?
Weight
Why does weight change?
Depending of the gravitational force/ field strength/ pull
What is displacement?
The distance covered in a straight line and has a direction
If cyclists maintain the same speed around a bend in the road, does the velocity stay the same?
Give a reason for your answer
No, the velocity will change
Because velocity is speed in a certain direction and as the cyclists go around the bend in the road they are changing both direction and therefore velocity
What do you measure weight in?
Newtons
What is mass measured in?
kg
Nano
1 X 10*-9
Micro
1 X 10*-6
Milli
1 X 10*-3
Kilo
1 X 10*3
Mega
1 X 10*6
Giga
1 X 10*9
Nano unit
n
Micro unit
u
l
Milli unit
m
Kilo unit
k
Mega unit
M
Giga unit
G
1cm =…m
0.01m
KE=
1/2 x m x v*2
GPE=
m x g x h
Independent variable
What you can change
Dependant variable
What you measure as a result of
Control variable
Any you keep the same
Repeats in experiments allow you to … (3)
Spot anomalies
Take a mean
So you can get more accurate results
What is a method?
A step by step guide of what to do to get good results. It must include VARIABLES, EQUIPMENT & PROCEDURE
Speed
= Distance/time
Acceleration =
Change in velocity/time
unit speed
m/s
unit for acceleration
m/s*2
Gradient of a distance-time graph
Speed
Gradient of a velocity-time graph
Acceleration
Area under the line on a velocity time graph
Distance
Earths acceleration due to gravity =
G= 10 m/s*2
Walking pace
1-2m/s
Running pace
5-8 m/s
What is the method for working out distance gone on a velocity time graph?
Area under the line
Efficiency =
Useful energy out/ total energy in
How can you work out the acceleration of gravity due to earth?
Drop weighted card from a certain point through a light gate to measure velocity
V =
Final velocity in m/s
U =
Initial velocity in m/s
x =
Distance travelled in m
Acceleration is
A measure of how fast velocity is changing
Speed is also known as
Velocity
What must be done to calculate speed at a driven time from a distance time graph for an accelerating object?
Draw a tangent to the curve at the required time
Calculate the gradient of the tangent
Give an equation relating final velocity with initial velocity, displacement and acceleration
V2=u2+ 2as
State a typical value for the speed of sound
330 m/s
What is the name given to the single force that is equivalent to all the other forces on a given object?
The resultant force
State Newton’s first law for a stationary object
If the resultant force on a stationary object is zero, the object will remain at rest
State Newton’s first law for a moving object
If the resultant force on a moving object is zero, the object will remain at a constant velocity (same speed in sma edirection)
State the defining equation for Newtons Second Law
Resultant force = mass X acceleration
State Newton’s second law in words
An objects acceleration is directly proportional to the resultant force acting on it and inversely proportional to its mass
What piece of equipment can be used to measure an objects weight?
A calibrated spring-balance or newton-meter
What is the resultant force that acts on an object moving in a circle called and in which direction does it act?
Centripetal force and acts towards the centre of the circle
What is inertial mass?
A measure of how difficult it is to change a given objects velocity
The ration of force over acceleration
State Newtons Third Law
whenever two objects interact, the forces that they expert on each other are always equal and opposite
State the equation used to calculate an objects momentum
Momentum = mass x velocity
What is the unit used for momentum ?
kgm/s
kilogram metres per second
In a closed system, what can be said about the momentum before and after a collision?
The total momentum before and after are equal
State an equation linking change in momentum, force and time
Force x time = change in momentum
How can you measure human reaction times?
Using a ruler drop test
What is the stopping distance of a vehicle equal to?
The sun of thinking distance and braking distance
For a given braking distance, if the vehicles speed is increased what can be said about its stopping distance?
The stopping distance is increases with an increase in speed.
Give a typical range of values for human reaction time
0.2 -0.9 seconds
Give 3 factors which can affect a drivers reaction time
- Tiredness
- Drugs
- Alcohol
Give 2 factors which may affect braking distance
- Adverse (wet/icy) road conditions
- Poor tyre/ brake conditions
Describe the energy transfers that take place when a car applies its brakes
Work is done by the friction force between the brakes and wheel
Kinetic energy of the wheel is converted to heat and is dissipated to the surroundings through the brake discs
To stop a car in given distance, if its velocity is increased, what must happen to the braking force applied?
The braking force must also be increased
State 2 consequences of a vehicle undergoing very large decelerations
- Kinetic energy converted to heat is very high causing brakes to overheat
- Loss of control of the vehicle
What is momentum?
A measure of how difficult an object is to stop- it is the product of the mass and velocity of a body.
What is the momentum equation?
Momentum = mass X velocity
p=mxv
What are the momentum units?
kgm/s
Is momentum a scalar or vector quantity?
Vector
What is the conservation of momentum?
The total momentum before is equal to the total momentum after
In a collision, momentum is..
Passed between objects- it is a conserved quantity
What are the 3 types of collision?
- Explosion
- Elastic
- Inelastic
The more time an impact takes…
The less force is exerted
Force =
Change in momentum / time
What is stopping distance?
The distance required to bring a car to a halt. It is split into thinking and braking distance
Stopping distance =
Thinking distance + Braking Distance
What is thinking distance?
The distance travelled during drivers reaction time
What affects thinking distance?
Alcohol/drugs
Tiredness
Mobile phone
Distraction
Eating/drinking
Age
What is braking distance?
The distance travelled once the brakes have been applied
What affects braking distance?
Speed
Icy roads
Poor tyres
Wet road
Speed
Mass
Car conditions
Worn brakes
State what is meant by an elastic collision:
Momentum and kinetic energy are conserved
State what is meant by an inelastic collision:
Momentum is conserved, kinetic energy is not.
In an explosion, the momentum must equal…
0
On a V-T graph, what does positive velocity and negative velocity mean?
Since velocity is a vector quantity, positive and negative velocity refer to direction.
