P10: Force/Mass/Acceleration (Y10 - Spring 1)

Question 1

🟢 What is a Force?

Answer 1

A force is a push or pull on an object. You cannot see a force but often you can see what it does.

Question 2

🟢 What do Forces do?

Answer 2

Forces can change the speed of something (speed up of slow down), the direction it is moving in or its shape (stretch or squash).

Question 3

🟢 What is meant by Acceleration?

Answer 3

Acceleration refers to an object’s change in velocity (either getting faster or slower). It is measured in m/s^2.

Question 4

🟢 What is meant by mass

Answer 4

Mass refers to the amount of a substance - the amount of matter in a substance/object. It is measured in kilograms (kg).

Question 5

🟢 How are Mass and Weight different?

Answer 5

Mass refers to the amount of a substance - the amount of matter in substance/object. It is measured in kilograms (kg).

Weight is the downward force exerted by an object due to it’s mass and the gravitational pull of a planet (or large body).

Weight = Mass x Gravitational Field Strength

Question 6

🟠 What is Inertia

Answer 6

The tendancy for an object to stay at rest or continue in uniform motion (constant velocity) is called inertia.

Inertial mass refers to the measure of difficulty in changing an object’s velocity.

An object with more mass has a greater tendancy to resist a change in it’s moving state. More force is required to move a greater mass from rest.

Question 7

🟠 What Newton’s 1st Law

Answer 7

‘An object will remain at rest or continue to move at a constant velocity unless a force acts on it.’

This is because object have inertia, which is a property of matter where by objects continue in their current state of motion, or at rest, unless the object is acted upon by an external force. Without a resultant force acting, a moving body will keep moving with constant velocity, and a body at rest will remain stationary. The greater the mass of a body, the more inertia it has.

Question 8

🟠 What Newton’s 2nd Law

Answer 8

‘A resultant force of 1N acting on a mass of 1kg will cause it to accelerate at a rate of 1m/s^2.’

This law is often written in equation form as: Force (N) = Mass (kg) x Acceleration (m/s^2).

Momentum can be related to force by the equation: Force(N) = Chnage in Momentum (kg m/s) / Change in Time (s)

Question 9

🟠 What Newton’s 3rd Law

Answer 9

‘For every action, there is an equal and opposite reaction’.

It is also useful to think of the law as ‘forces always come in pairs’

It is also important to realise for this ‘interaction pair’ of force that:

• Each force acts on a different object
• The two forces are the same size
• The two forces are in opposite directions
• The two forces are the same type.

Question 10

🟠 What is ‘Stopping Distance’?

Answer 10

Your stopping distance is equal to your thinking distance + braking distance.

Stopping Distance = Thinking Distance + Braking Distance

The distance it takes to stop a moving car is divided into two factors: the thinking and braking distance.

Question 11

🟠 What is ‘Thinking Distance’

Answer 11

The thinking distance is the distance travelled in between the driver realising he needs to brake and actually breaking (It takes time for a driver to react to a situation. During this reaction time the car carries on moving.)

Question 12

🟠 What is ‘Braking Distance’

Answer 12

The braking distance is the distance taken to stop once the brakes are applied.

Question 13

🟠 Personal Factors that affect the Thinking Distance are:

Answer 13

1. How fast the car is going.
2. How intoxicated the person is (drink/drugs)
3. Concentration of the person (tiredness)
4. Poor visibility

Question 14

🟠 External Factors that affect the Braking Distance are:

Answer 14

1. The speed of the vehicle.
2. The mass of the vehicle.
3. The condition of the brakes
4. The condition of the tyres (tread)
5. The condition of the road (weather)

Question 15

🟠 How to convert from mph to m/s and back equation, Speed equation, Acceleration equation, Stopping Distance equation, and Force equation

Answer 15

• To convert from m/s to mph (miles per hour) multiply by 2.2
• To convert from mph to m/s, divide by 2.2
• Speed (m/s) = Distance Travelled (m) / Time Taken (s)
• Acceleration (m/s2) = Change in Velocity (m/s) / Time Taken (s)
• Stopping Distance (m) = Thinking Distance (m) + Braking Distance (m)
• Force (N) = Mass (kg) x Acceleration (m/s^2)

Question 16

🟢 Worked example
Two ice hockey players skate towards the puck. The players are travelling in opposite directions. They collide and fall over, coming to a stop. Using the information below, calculate the initial velocity of player B.

Player A:
Mass = 90kg
Velocity = 5m/s

Player B:
Mass = 85kg
Velocity = ?

Answer 16

Step 1 Momentum after the collision = 0 kg m/s (both players fall over)

Step 2 Remember that player B is moving to the left so will have a negative
velocity and player A has a positive velocity.
Momentum before the collision = (mass player A x velocity player A) + (mass player B x velocity player B)

= 90 x 5 - 85 × v
= 450 - 85v

Step 3 Law of conservation of momentum states momentum before the collision = momentum after the collision

450 - 85 × v = 0
450 = 85 v

Dividing by 85:
v = -5.2941176 or -5.29 (to 3 significant figures).

This means that Player B had a velocity of 5.29 m/s to the left before the collision.

Question 17

🟢 What is Momentum

Answer 17

A moving object has momentum - this is the tendancy of the object to keep moving in the same direction.

It is difficult go change the direction of movement of an object with a lot of momentum.

Momentum (kg m/s) = Mass (kg) x Velocity (m/s)
(p=mv)

Momentum has both a magnitude and direction (dependant on the velocity of the object)

Question 18

🟢 Explain Conservation of Momentum

Answer 18

In a ‘Closed System’, the total momentum before an event is equal to the momentum after the event.

As momentum is conserved in the mass, velocity or momentum of an object in an explosion or collision can be worked out.

Question 19

🟢 What happens if a vehicle collides with another vehicle of the same mass (or two of the same mass)?

Answer 19

If a vehicle collides with another vehicle of equal mass - the velocity of vehicle A is halved by the impact, but the combined mass after the colision is twice the moving mass befire the collision, meaning the momentum remains.

For a single vehicle colliding into two vehicles, the velocity of vehicle A is reduced to one third, but the combined mass after the collision is three times the initial mass, meaning the momentum remains.

Question 20

🟢 Equations for Calculating Momentum (as well as the showing the Conservation of Momentum in explosions/collisions)

Answer 20

M1 U1 + M2 U2 =M1V1 + M2V2

Also, always remember: Momentum Before = Momentum After.

For Conservation of Momentum in explosions/collisions:

(Mass A x Velocity A) + (Mass B x Velocity B) = 0
so,
(Mass A x Velocity A) = (Mass B x Velocity B)

Question 21

🟢 Describe the forces acting on a Skydiver, and how they reach their Terminal Velocity

Answer 21

A Skydiver:

1. At the start of his jump, the air resistance is small so he accelerates downwards.
2. The the diver’s velocity increases, his air resistance will increase
3. Eventually, the air resistance will be big enough to equal the skydiver’s weight. At this point, the forces are balanced, so his speed becomes constant - This is called Terminal Velocity

When the Parachute is Opened:

4. When the diver opens his parachute, the air resistance suddenly increases, causing his to start slowing down.
5. Because he is slowing down, his air resistance will increase again until it balances his weight. The skydiver has now reached a new, lower, Terminal Velocity.

Question 22

🟠 How is the Braking Speed affected by the Starting Speed? (Explanation and Equations)

Answer 22

One thing that is important to note, is that the Thinking Distance is proportional to the starting speed. This is because the reaction time is taken as a constant, and distance = speed x time. This is why the stopping distances exponentially change so noticeably.

The Braking Distance increases four times each time the starting speed doubles. This is due to the work done in bringing a car to rest, meaning the kinetic energy needs to be removed. Therefore:

W = F x D (Work Done = Braking Force x Distance),
KE = 1/2 x m x v^2 (Kinetic Energy = 1/2 x Mass x Velocity^2)

These two equations as a result mean that the braking force is
proportional to the square of the velocity, linked by the
equation:

F x d = 1/2 x m x v^2

Question 23

🟠 How does Wet Conditions affect Stopping Distance

Answer 23

When driving in wet conditions or in rain the Highway Code advises your total stopping distance will be at least double the distance to stop on a dry surface.

Furthermore, research has shown that at 30mph on a wet road, a car with tyres featuring 8mm of tread can come to a stop in 25.9 metres. This is currently under a meter taken to stop per mph travelled, but when you are then travelling in the same conditions at the same speed, a car with tyres with 3mm of tread will take 35 metres to come to a complete stop. This is now a good 5 meters over the meter take to stop per mph, which just shows how the traction and tread of the tyre can affect braking in a vehicle, especially when the tread is as fine as 1.6mm, the stopping distance increases up to as far as 43 metres, which is far, far over the distance it takes to stop in the wet with 8mm tread.

This not only shows how the much tread affects the stopping distance, especially in the rain, but when you compare the average time it takes for a car to stop in the rain to that of ice and on the other side of the scale in the completed dry, you get an overall sense of how small changes like that of the tread or the weather can really make a big difference.

Question 24

🟠 How does Icy Conditions affect Stopping Distance (+What Should You Do If Your Driving On Ice)

Answer 24

When driving in conditions of ice and snow the Highway Code advises your braking distance could be up to Ten Times higher than it would be on dry road. As a result, the equation for stopping in ice is:
Total Stopping Distance (In Ice) = Thinking Distance + (Stopping Distance x10)
That mean if you are travelling 70mph on icy road it could take you up to as long as 771m to fully stop of the car. This is the equivalent of half a mile, or the length of 8 full size football pitches.

What Should You Do If Your Driving On Ice:

As a result of what is mentioned above above you should be extremely careful when driving on ice, whilst making a conscious effort to not accelerate or turn too suddenly, as you can easily spin out of control and possibly cause a major accident, but certainly not to be travelling at any kind of high speed at all. Also, like mentioned in the previous slide, the traction and grip of your tyres as a result of their tread will also be vital in terms of keeping as much grip and control as possible also.

Question 25

🟠 What is a Crumple Zone and What Does It Do To Protect Passengers? (+ Who Made It and When)

Answer 25

The Crumple Zone, or ‘Crash’ zone is a structural safety feature of a car, or vehicle, which increases the time over which a change in velocity is able to occur from the impact of a crash, essentially absorbing most of the energy and shockwaves from the impact. There a two crumple zones in cars, and these are located at the very front, and very back of the car (as this is the most probable place in which you’re going to get hit). These two zones essentially protect the passenger cell, or driving compartment from getting damaged as much as possible.

A man called Béla Barényi was the person who first created the crumple zone for Daimler-Benz. One of his 2,500 patents, issued in 1952, explains how a car could be designed with areas at the front and rear built to deform and absorb kinetic energy in an impact. He put the concept to use in 1959 on the Mercedes-Benz W111b.

Question 26

🟠 What is are Seatbelts and What Does It Do To Protect Passengers? (+ Who Made It and When)

Answer 26

The seatbelt is a vehicle safety device that is designed to secure the driver and the passenger in their place, and therefore protect them and keep them in their seats, instead of flying straight through the windscreen/windows in the event of any any sudden movement that could be from an unexpected stop, or through a collision.

In addition, seatbelts are also very effective, as it is reported that among drivers and front seat passengers, the risk of death in a crash reduced by 45% and in terms of serious injuries by 50% when the seatbelts are being worn properly, with people who do not wear seatbelts being 30 times more likely to be ejected from the vehicle during a crash.
The first seatbelt made was invented by the English Engineer George Cayley, who created the seatbelt to keep pilots inside of their gliders, with the first ever patented seatbelt being released by Edward J. Claghorn on February 10, 1885 to keep tourists safe in taxis.

Question 27

🟠 What is are Airbags and What Does It Do To Protect Passengers? (+ Who Made It and When)

Answer 27

The Airbag in technical terms is a ‘vehicle occupant-restraint system’ that uses a bag that is designed to inflate very, very quickly, and then deflate during a collision. Consequently, this means that you are partly protected from the initial impact of the crash, as the airbag has inflated by the time you jolt into, but deflated by the time the initial impact has passed. This nylon bag also reduces the chances of the driver and passengers of colliding and hurting each other in the crash, because the movement is so restricted when the airbag is deployed. The things that make up a fully functioning airbag system are the flexible fabric bag, an inflation module, and an impact sensor.

Air bags (then called Air-Filled Bladders) were in use as early as the 1950’s, and were specifically created for automobile use by John W. Hetrick, who successfully filled his airbag patent on 5th August 1952. From here onwards, the airbag has been used in many, many cars and vehicle all over the world, whilst saving many lives too.

Question 28

🟠 What Do Advanced Driver Assistance Systems (ADAS’s) Do?

Answer 28

ADAS systems can help the driver either while driving at speed, reversing, or parking and all contribute in some way to avoiding a collision. Some examples of features are as follows:

• Adaptive Cruise Control
• Automatic Emergency Braking
• Blind Spot Detection
• Collision Warning
• Cross-Traffic Alert
• Forward and Rear Collision Warning
• Lane Departure Warning
• Pedestrian Detection System
• Road Sign Recognition

These ‘Advanced Systems’ use cameras and sensors to be able to detect certain hazards and potential collisions, and alert the driver them, as a result, making these features important safety features to prevent accidents

Question 29

🟠 Do Advanced Driver Assistance Systems (ADAS’s) Really Make A Difference (+ The Downsides)

Answer 29

Most studies done with ADAS tell us that they do in fact make driving safer, for example, the crash involvement rate for vehicles with blind spot monitoring was 14% lower than the same models without this equipment. The same study also came back with the suggestion of if every vehicle sold in the USA was equipped with blind spot monitoring, then 50,000 crashes and 16,000 injuries would’ve been avoided.
Furthermore, other studies say that a combination of vehicle crash avoidance technologies reduce the likelihood of crashing by 3.5%, would see savings of up to $264 billion, assuming all relevant crashes are prevented through vehicle crash avoidance technologies in light vehicles.

The Downsides:
On the other hand, the systems that are in place are by no means perfect, and still have a long way to go until they are improved to their maximum. Some examples of a system going wrong is when the car can sometimes misread a vehicle in the other lane as one you’re about to crash into, or a ramp in front of you as a brick wall, so it applies the emergency brakes. So in summery, although this is advanced technology, cars having AI safety features still has a long way to until they are as effective and streamlinef as they can be.

Question 30

🟠 How is Impact affected by Impact Time

Answer 30

The longer the impact time, the more the impact is reduced.

Force (N) = Mass (kg) x Change in Velocity / Time Taken (s)

Question 31

🟢 What is an Elastic Object

Answer 31

An elastic object is one which regains its shape when the forces deforming it (e.g stretching or squashing) are removed.

When an elastic object is deformed the energy which caused it to deform is stored as elastic energy, which is released when the force is removed.

Question 32

🟢 What is Compression

Answer 32

When a force is exerted down on an object (a spring for example) it will be compressed (push the spring together).

This means that in Compression, the particles making up the material are pushed closer together.

Question 33

🟢 What is Tension

Answer 33

As well as compression an object (spring for example) can be in tension, this is when a force pulls out on the object (stretching a spring).

This means when an ibject is under tension, the particles making the material are pulled further apart.

Question 34

🟢 What is something when it is Proportional

Answer 34

If something proportional, it is:

• Corresponding in size or amount to something else
• A variable quantity having a constant ratio to another quantity.

Question 35

🟢 What is Hooke’s Law (+ Equation and the meaning of the Limit of Proportionality)

Answer 35

The extension of a spring is directly proportional to the force appiled, provided its limit of proportionality is not exceeded.

Force Applied = Spring Constant x Extension
F (N) = k (N/m) x Δe (m)

What does the ‘Limit of Proportionality’ mean?
This means that the material starts to behave in a non-linear way. The material will no longer continue to deform and be able to regain its original shape.