SP2: Forces and Motion

Question 1

How do you calculate the resultant force?

Answer 1

• If the two forces are in the same direction, you add them and state their direction
• if the two forces are in opposite directions, subtract the smaller force from the bigger one and state the direction of the bigger one

Question 2

When are the forces on an object balanced?

Answer 2

When the resultant force is 0

Question 3

What is Newton’s first law?

Answer 3

An object remains in the same state of motion unless acted upon by a resultant force

Question 4

What does it mean if the resultant force on an object is 0?

Answer 4

• stationary objects remain stationary
• a moving object continues to move at the same velocity

Question 5

What is Newton’s Second Law?

Answer 5

Force = mass x acceleration

Question 6

What does Newton’s Second Law show?

Answer 6

It shows the acceleration of an object is:
- proportional to the resultant force of the object
- inversely proportional to the mass of the object

Question 7

What is inertial mass?

Answer 7

How difficult it is to change the velocity of the object. It is defined as the ratio of force over acceleration

Question 8

Define mass

Answer 8

The quantity of matter in an object

Question 9

What is used to measure force?

Answer 9

A forcemeter

Question 10

What are the units of force?

Answer 10

Newtons

Question 11

What is weight

Answer 11

The measure of the pull of gravity

Question 12

How do we calculate weight?

Answer 12

mass x gravitational field strength

Question 13

What is the unit for gravitational field strength on Earth?

Answer 13

N/kg

Question 14

What is the quantity of gravitational field strength on Earth?

Answer 14

9.8 N/kg

Question 15

What does the acceleration of the resultant force depend on?

Answer 15

• the size of the force (for the same mass, the bigger the force, the larger the acceleration)
• the mass of the object ( for the same force, the more massive the object, the smaller the acceleration)

Question 16

What is Newton’s third law?

Answer 16

Whenever two objects interact, they exert an equal and opposite force onto each other

Question 17

What do the forces have to do for Newton’s third law to prove true?

Answer 17

• act on two different types of objects
• are the same type of force (eg contact force)

Question 18

What are action-reaction forces?

Answer 18

A pair of forces that:
- act on two different bodies
- forces exerted are of equal size
- act in opposite directions
- same size
- the same type of force (contact/ non contact)
- Act in the same line of action

Question 19

What is the equation to measure inertial mass?

Answer 19

force/ acceleration

Question 20

Define normal contact forces

Answer 20

The force that surfaces exert to prevent solids from passing through each other. This only happens on contact

Question 21

Define momentum

Answer 21

The tendency of an object to keep moving, or how hard it is for it to stop moving

Question 22

What are the two factors momentum is dependant on?

Answer 22

mass and velocity

Question 23

What is the equation for momentum?

Answer 23

mass x velocity

Question 24

What are the units for momentum?

Answer 24

kg m/s

Question 25

What is the conservation of momentum?

Answer 25

The total momentum before a collision is the same as the total momentum after the collision

Question 26

When is the conservation of momentum possible?

Answer 26

In a closed system

Question 27

How is momentum conserved?

Answer 27

In collisions and explosions

Question 28

Using Newton's third law, describe the collision of two marbles and the effect they will have on each other

Answer 28

- two marbles will collide - the force exerted by marble a onto marble b will be the same as that exerted by marble b onto marble a

Question 29

How can we combine Newton's second law with momentum?

Answer 29

force = (change in momentum)/ time

Question 30

Define stopping distances

Answer 30

Sum of breaking and thinking distance

Question 31

Define breaking distance

Answer 31

Distance the driver travels when the breaks have been applied

Question 32

Define thinking distance

Answer 32

Distance driver travels when acknowledging the situation

Question 33

What is a reaction time?

Answer 33

Time between a person detecting a stimulus and their reaction

Question 34

What factors affect reaction times?

Answer 34

- distractions - fatigue - illness - consumption of drugs or alcohol

Question 35

How can we measure someone's reaction time?

Answer 35

Using the ruler drop test

Question 36

Describe the ruler drop test

Answer 36

Dropping a ruler between someone's thumb and forefinger, with the 0 cm facing downwards. The higher the reaction time needed to grasp the falling ruler, the further the ruler falls before being stopped.

Question 37

Give some examples of factors affecting thinking distance

Answer 37

- speed of car - tiredness - drugs and alcohol - medication

Question 38

What can increase the braking distance of a car?

Answer 38

- poor road and weather conditions - poor vehicle conditions, eg: worn tires or brakes, which reduces the friction between the tire and brake - more mass in the vehicle, the brakes have to travel a large distance to remove the large kinetic energy

Question 39

Define work done

Answer 39

The amount of energy it takes to do a task

Question 40

What are the units for work done?

Answer 40

Joules (j)

Question 41

How are speed and braking distance related?

Answer 41

The greater the speed, the greater the braking distance

Question 42

What is the danger of a large deceleration?

Answer 42

The force can cause injury

Question 43

Describe a large deceleration during a crash in terms of momentum

Answer 43

- Before the crash, you have a large momentum, due to a large velocity - After you crash, you are stagnant and therefore have no momentum - so a greater force is felt

Question 44

What is the equation for work done?

Answer 44

force x distance

Question 45

What safety features are present in cars to reduce the effects of a large force during a crash?

Answer 45

- seat belts - traction control - anti-block brakes - crumple zones - electric windows - safety cage - paddle shift controls - air bags

Question 46

What are active safety features?

Answer 46

These actively occur at a car crash, such as seatbelts, air bags and crumple zones

Question 47

How do active safety features work?

Answer 47

They change shape during the crash to absorb all the energy. This: - reduces injuries - reduces the rate of change of momentum - force exerted from the driver decreases

Question 48

What is work done in a vehicle related to?

Answer 48

The initial kinetic energy of the vehicle

Question 49

What is the average mass of a car?

Answer 49

1500kg

Question 50

Define large deceleration

Answer 50

Slowing down or a negative acceleration

Question 51

What are the effects of a large deceleration?

Answer 51

- cause the brakes to overheat - driver may lose control of the brakes