Motion Graphs and Forces Flashcards
what does the gradient represent on a distance/time graph?
the gradient is equal to the speed of the object (velocity)
what is the equation for speed?
distance ÷ time
what is the equation for the average speed?
total distance ÷ total time
what does the gradient of a velocity/time graph represent?
the gradient is equal to the acceleration of the object
how do you work out the distance travelled on a velocity/time graph?
look at the area under the gradient
e.g. if it makes a triangle under the line you then do 1/2 x base x height to work out the distance
what is the units for velocity?
m/s
what is the units for acceleration?
m/s2
if a ticker tape timer produces dots at a frequency of 50Hz, how many dots are produced per second?
50
on a ticker tape timer, how can you tell if the dots are moving at a constant speed?
the dots are equally spready apart
on a ticker tape timer, how can you tell if the dots accelerating?
the dots will get further apart
on a ticker tape timer, how can you tell if the dots decelerating?
the dots will get closer together
what is aceleration?
the rate of change of velocity
rate of change = 1/t
what is the equation for acceleration?
a = v - u ÷ t ( v = final velocity, u = initital velocity)
change in velocity ÷ time taken
a = Δv ÷ t = m/s x 1/s = m/s2
how do velocity and acceleration act in decelration?
in opposite directions causing the velocity to get smaller
what is a scaler quantity?
quantities that have magnitudes or a size only
what is a vector quantity?
quantities that have magnitude and direction
give some examples of scalars
mass
temprature
distance
time
speed
energy
give some examples of vectors
velocity
force
weight
what is Newton’s first law?
objects will remain at rest or continue to move at a constant speed unless acted upon by a resultant force
if F=0 a =0m/s2
(F = resultant force)
what is Newtons second law?
resultant force is directly proportional to the rate of change of momentum
F∝ mv - mu ÷ t
(F = resultant force, ∝ = directly proportional, t = rate of change, mv - mu = momentum)
F = mv-mu ÷ t
F = m (v-u) ÷ t [acceleration]
F= ma
resultant force = mass x acceleration
what are the units used in the equation for Newton’s second law?
resultant force = mass x acceleration
F = ma
F = resultant force (N)
m = mass (kg)
a = acceleration (m/s2)
what is static friction?
the friction acting on stationairy objects
what is dynamic friction?
the friction acting on moving objects
what is the control variable?
something that is constant and unchanged
what is thinking distance?
the distance a vehicle travels while the driver is reacting
what is breaking distance?
the distance a vehicle travels while the brakes are being applied until it stops
what is stopping distance?
thinking distance + breaking distance
give some factors that affect thinking distance
use of alcohol
use of drugs (il/legal)
distracted by passengers in the vehicle
tired
using a mobile
speed of car
give some factors that affect braking distance
mass of car
weather
tread of tyres
wornout breakes
level of grip on road
speed of car
if the distance = 8,000m and the time = 3,600s, calculate the average speed
average speed = total distance ÷ total time
= 8000 ÷ 3600
=2.2 m/s
describe the motion of a on this distance/time graph
a is stationairy because the gradient is a straight, vertical line
we did not move it we just let the device play
describe the motion of e on this distance/time graph
e is accelerating away from the origin
there is no constant speed
we started the pencil case at the device (origin) and then accelerated it away
describe the motion of b and c on this distance/time graph
b is moving fast at a constant speed
c is moving fast at a consant speed but faster than b, almost double
to achieve this graph we flipped the sensor from its side to face upwards and we moved a pencil case upwards and away from it in a constant motion
describe the motion of f on this distance/time graph
f is movimg at a fast away from the device (origin) and constant pace but then remains stationairy at a point
describe the motion of a on this velocty/time graph
a is moving at a constant speed
describe the motion of d on this velocity/time graph
d is deccelerating at a constant rate
describe the motion of b and c on this velocity/time graph
b is acelerating at a constant rate
c is acelerating at a constant rate faster than b
in equilibrium or when stationionairy or moving a constant speed, what is the resultant force?
0N
calculate the resultant force and the accelertaion of this 5.0kg mass
F = 1050-895
= 155N (downwards)
as F = ma
a = F ÷ m
= 155÷5
= 31 m/s2
calculate the resultant force and the accelertaion of this 5.0kg mass
F = 100 + (-80)
= 20N (to the left)
as F = ma
a = F ÷ m
= 20 ÷ 5
= 4 m/s2 (to the left)
calculate the resultant force and the accelertaion of this 5.0kg mass
F = 10 + (-15)
= 5N (downwards)
as F = ma
a = F ÷ m
= 5 ÷ 5
=1 m/s2
calculate the resultant force and the accelertaion of this 5.0kg mass
F = 100 + (-500)
= 400N (downwards)
as F = ma
a = F ÷ m
= 400 ÷ 5
=80m/s2 (downwards)
what is the reaction time of the driver?
0.6 seconds
calculate the thinking distance
area of the rectangle (imagine this)
20 x 0.6
= 12m
how long did the car brake for?
2.8-0.6
= 2.2 secs
calculate the braking distance
area of triangle
0.5 x 20 x 2.2
= 22
calculate the stopping distance if it has been previously worked out that the thinking distance is 12m and the braking distance is 22m
22 + 12
= 34m
in terms of energy, what do brakes do to a car?
original kinetic energy = 400,000J
final kinetic energy = 0J
kinetic energy is converted into heat and sound which is then disipitated into the atmosphere
the brake pads do work
kinetic energy –> heat + sound
if Fd = change in Ek, calculate the average braking force (F) produced by the brakes
kinetic energy = 400,000J
braking distance = 22m
d = braking distnace = 22
Ek = 400,000J
F = Ek ÷ d
= 400,000 ÷ 22
= 18181.81 N
when giving an acceleration, what must it have?
a direction
e.g. downwards, to the left
complete this skydiver velocity/time graph
state the value or direction of the resultant force at A
Resultant force is acting dowanwards because weight is the only force acting on the sky diver
towards the ground (downwards)
state the value or direction of the resultant force at B
resultant force is decreasing yet it still acting downwards because air resistance is increasing
state the value or direction of the resultant force at C
resultant force is zero
the skydiver has reached terminal velocity
because the graident and acceleration is zero
state the value or direction of the resultant force at D
resultant force is acting upwards (velocity acting down, accelerating upwards)
because he is rapidly deccelertaing
state the value or direction of the resultant force at E (end of graph parachute)
resultant force is zero as the sky diver has reached a new terminal velocity
because the gradient and acceleration is zero
the weight of an object is the force of ……which acts on it
gravity
when you drop something, first of all it …..
acelerates
the faster an object falls, the bigger force of ……. which acts on it
friction
eventually a dropped object will …….
fall at a steady speed
which force is the foward force from the engine?
which force is the force resisting the van’s motion?
A is the foward force
E is the force resisting motion
complete this table
complete the following paragraph to explain why seatbelts reduce the risk of injury if the van stops suddenly
a large …. is needed to stop the van suddenly
the driver and passengers would continue to move …..
the seatbelts supply a …. force to keep the driver and passengers in their seats
a large force is needed to stop the van suddenly
the driver and passengers would continue to move fowards
the seatbelts supply a backwards force to keep the driver and passengers in their seats
if the mass of a car is 950kg and the car can accelerate from 0 to 33m/s in 11 seconds, calculate the acceleration of the car during the 11 scesonds
a = v-u ÷ t
= 33 - 0 ÷ 11
= 3m/s2
if the mass of a car is 950kg and the car can accelerate from 0 to 33m/s in 11 seconds, calculate the force needed to produce this acceleration
F = ma
= 950 x 3
=2850 N
The manufactor of a car claims a top speed of 110 miles per hour. Explain why there must be a top speed for a car
the air resistance will increase directly proportionally to the speed
the car cannot accelerate forever, it must reach a resultant force
everntually the engine force will = air resistance
a driver may have to make an emergency stop
give three factors which affect their thinking distance or braking distance
use of alcohol affects thinking distance as it slows down you reaction time. this affects your stopping distance as stopping distance = thinking + braking distance. if your thinking distance increases, so will your stopping distance
being distracted by the passengers in the car will affect thinking disatnce as you aren’t focused and your reaction time is delayed - this increased stopping distance as they are connected
worn out brakes will affect your braking distances as the efficiency of the brakes decreases . friction will act in opposite motion to the tyres, increasing the braking distance. as braking distance increases, so does stopping
what does the acceleration of a car depend on?
the force applied by the engine and the mass of the car
the velocity of a car is its speed in a particular ……
direction
what part of the graph represents thinking time of the driver and what is this time in seconds?
A - B
0.7 seconds
calculate the distance travelled by the car in thinking time
area of rectangle
0.7 x 24
= 16.8m
calculate the acceleration of the car after the brakes are applied
a = v - u ÷ t
= 24 ÷ t
= -6 m/s2
calculate the distance travelled by the car during braking
are under the traingle
4x 24 ÷ 2
= 48m
the mass of the car is 800kg
calculate the braking force
F = ma
= 800 x -6
= - 4800 N
Explain the motion of a skydiver
Before the parachute opens:
- When the skydiver jumps out of the plane he accelerates due to the force of gravity pulling him down.
- As he speeds up the upwards air resistance force increases. He carries on accelerating as long as the air resistance is less than his weight.
- Eventually, he reaches his terminal speed when the air resistance and weight become equal. They’re said to be balanced.
After the parachute opens:
- When the canopy opens it has a large surface area which increases the air resistance. This unbalances the forces and causes the parachutist to slow down.
- As the parachutist slows down, his air resistance gets less until eventually it equals the downward force of gravity on him (his weight). Once again the two forces balance and he falls at terminal speed. This time it’s a much slower terminal speed than before.
Look In Experiment Write-Ups:
describe an experiment to investigate friction
Define resultant force
the sum forces acting on an object
What is the equation that links gravity, mass and weight?
weight (N) = mass (kg) x gravity (N/kg)
What are the units for force?
Newtons (N)
What are the units for acceleration?
Metres per second2 (m/s2)
What are the units for gravity?
Netwong per kilogram (N/kg)
What are the units for mass?
Kilograms (kg)
A force is simply a … or a …
A force is simply a push or a pull
What are the twelve different types of forces you need to know?
gravity
weight
reaction force
electrostatic force
thrust
push
pull
drag
air resistance
friction
lift
tension
Gravity or weight always act …
Gravity or weight always act straight downwards
Reaction force from a surface usually acts …
Reaction force from a surface usually acts straight upwards
The direction of electrostatic force between two charged objects depends on …
The direction of electrostatic force between two charged objects depends on the type of the charge (like charges repel, opposite charges attract)
Thrust or push or pull speeds/slows something up/down
Thrust or push or pull speeds something up
Drag or air resistance or friction speeds/slows something up/down
Drag or air resistance or friction slows something down
Lift acts on …
Lift acts on aeroplane wings
Tension acts in a … or …
Tension acts in a rope or cable
What four forces are acting on a moving car?
If an object has no force propelling it foward, it will always slow down and stop because of …
If an object has no force propelling it foward, it will always slow down and stop because of friction
What is friction?
friction is a force that opposes motion
In what three main ways does friction occur?
Friction betwen solid surfaces which are gripping (static friction)
Friction between solid surfaces which are sliding past each other
Resistance or ‘drag’ from fluids (liquids or gases)
How do you reduce:
Friction betwen solid surfaces which are gripping (static friction)
Friction between solid surfaces which are sliding past each other
by putting a lubricant, like oil or grease, between the surfaces
In a fluid, friction always increases as the speed …
In a fluid, friction always increases as the speed increases
Explain how moving objects reach a terminal velocity
Wehn objects first set off they have much more force accelerating them than resistance slowing them down
As the velocity increases, the resistance increases
This gradually reduces the acceleration until eventually the resistance is equal to the accelerating force and then it won’t be able to accelerate any more - it will have reached its terminal velocity
How can you investigate falling objects using sycamore seeds?
- Sycamore seeds have a small wieght and a large surface area so they reach terminal velocity really quickly and fall slowly
- Collect a bunch of sycamore seeds of different sizes and measure the mass and wing length of each one. Use an accurate ruler and repeat each measurement several times to make sure it’s accurate. Use all the seeds that have similar masses but different wavelengths
- Drop each of the seeds from the same height and use a stopwatch to find how long each one takes to fall to the ground. The higher you drop them the better - it gives a larger measurement and so improves the accuracy of the measurement
- Repeat the experiment for each seed and find an average time
- Plot a graph of length of the wings (x) against the time taken to hit the floor (y). This will tell you if there is a relationship between the shape of the sycamore seeds and their terminal velocity
- Bigger wings means bigger surface area and so higher drag. Higher drag means lower terminal velcoty, and so the seeds fall more slowly
Explain the relationship between drag (air resistance) and weight during terminal velocity
during terminal velocity, weight = drag (air resistance)
What is Newton’s Third Law?
if object A exerts a force in object B then object B exerts the exact opposite force on object A
Objects … when the resultant force is positive
Objects … when the resultant force is negative
Objects accelerate when the resultant force is positive
Objects decelerate when the resultant force is negative
Be able to describe the motion of objects on a distance/time graph
Be able to describe the motion of objects on a velocity/time graph
Describe an experiment to investigate the motion of a toy car on a ramp
- Mark a line on the ramp - this is to make sure the car starts from the same point each time
- Measure the distance between each light gate - you’ll need this to find the car’s average speed
- Let go of the car just before the light gate so that it starts to roll down the slope
- Let go of the car just before the light gate so that it starts to roll down the slope
- The light gates should be connected to a computer. When the car passes through each light gate, a beam of light is broken and a time is recorded by a data-logging software
- Repeat this experiment several times and get an average time for the car to reach each light. This will make your results more reliable
- Using these times and distances between lightgates you can find the average speed of the car on the ramp and the average speed of the car on the runway
