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/s^{2}

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/s^{2}

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/s^{2}

(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/s^{2})

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/s^{2}

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/s^{2} (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/s^{2}

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/s^{2} (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/s^{2}

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/s^{2}

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:**

1. When the skydiver jumps out of the plane he accelerates due to the force of gravity pulling him down.

2. 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.

3. Eventually, he reaches his terminal speed when the air resistance and weight become equal. They're said to be balanced.

**After the parachute opens:**

4. 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.

5. 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 second^{2} (m/s^{2})

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?

1. Sycamore seeds have a small wieght and a large surface area so they reach terminal velocity really quickly and fall slowly

2. 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

3. 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

4. Repeat the experiment for each seed and find an average time

5. 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

6. 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

1. Mark a line on the ramp - this is to make sure the car starts from the same point each time

2. Measure the distance between each light gate - you'll need this to find the car's average speed

3. Let go of the car just before the light gate so that it starts to roll down the slope

4. Let go of the car just before the light gate so that it starts to roll down the slope

5. 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

6. Repeat this experiment several times and get an average time for the car to reach each light. This will make your results more reliable

7. 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