Topic 5 - Forces

Question 1

What is a vector quantity?

Answer 1

it has magnitude and direction

Question 2

Give examples of vector quantities (5)

Answer 2

• force
• velocity
• displacement
• acceleration
• momentum

Question 3

What is a scalar quantity?

Answer 3

only has magnitude and no direction

Question 4

Give examples of scalar quantities (7)

Answer 4

• mass
• speed
• distance
• time
• energy
• power
• density

Question 5

What is the equation to calculate weight?

Answer 5

mass x gravity

Question 6

What will happen to an object with NO resultant force acting on it?

Answer 6

either:
- remain stationary
- remain at a constant velocity

Question 7

What will happen to an object with a resultant force acting on it?

Answer 7

accelerate - it could be:
- speeding up
- slowing down
- changing direction

Question 8

Define a resultant force

Answer 8

one force representing multiple forces

Question 9

Define elastic deformation

Answer 9

the object can go back to its original shape after the force has been removed

Question 10

Define inelastic deformation

Answer 10

the object cannot go back to its original shape - it has been permanently deformed

Question 11

When does inelastic deformation occur?

Answer 11

when the limit of proportionality is exceeded

Question 12

What is Hooke’s Law?

Answer 12

The extension of an object is directly proportional to the force applied to it, provided the limit of proportionality hasn’t been exceeded

Question 13

What is the law of conservation of energy?

Answer 13

energy cannot be created or destroyed, only transferred

Question 14

A moment depends on 2 things:

Answer 14

• the perpendicular force
• the perpendicular distance

Question 15

What is the principle of moments?

Answer 15

for a system in equilibrium, the sum of the clockwise moments is equal to the sum of the anticlockwise moments

Question 16

What is a moment?

Answer 16

the turning effect of a force

Question 17

Define speed

Answer 17

the rate of change of position

Question 18

Define velocity

Answer 18

the rate of change of position in a given direction

Question 19

What is the average walking speed?

Answer 19

1.5 m/s

Question 20

What is the average running speed?

Answer 20

3 m/s

Question 21

What is the average cycling speed?

Answer 21

6 m/s

Question 22

Define acceleration

Answer 22

the change in velocity in a certain amount of time

Question 23

On a velocity-time graph, what does the gradient of the line represent?

Answer 23

acceleration

Question 24

On a distance-time graph, what does the gradient of the line represent?

Answer 24

speed

Question 25

How do you find distance on a velocity-time graph?

Answer 25

the area under the graph

Question 26

What is drag?

Answer 26

the resistance you get in a fluid

Question 27

How do you reduce drag?

Answer 27

keeping the shape of the object streamlined

Question 28

Why will an object slow down and stop if it has no force propelling it?

Answer 28

friction

Question 29

Describe an object falling

Answer 29

- when it first sets off, the force of gravity is much more than the frictional force slowing it down, so it accelerates - as the speed increases, the friction builds up - this gradually reduces the acceleration until the frictional force is equal to the accelerating force (so the resultant force is zero) - it will have reached its terminal velocity and will fall at a steady speed

Question 30

Define terminal velocity

Answer 30

the maximum speed of an object, reached when the forces moving the object are balanced by its frictional forces

Question 31

Name Newton's 1st law

Answer 31

if an object has no resultant force, it will continue to move at a constant velocity or remain stationary

Question 32

Name Newton's 2nd law

Answer 32

resultant force = mass x acceleration - acceleration is directly proportional to the resultant force - acceleration is inversely proportional to the mass

Question 33

Name Newton's 3rd law

Answer 33

when two objects interact, the forces they exert on each other are equal and opposite

Question 34

Define stopping distance

Answer 34

- the distance travelled between seeing the obstacle and the car reaching 0 m/s - thinking distance + braking distance

Question 35

Define thinking distance

Answer 35

the DISTANCE travelled between seeing the obstacle and applying the brakes

Question 36

Define braking distance

Answer 36

the DISTANCE travelled between applying the brakes and the car reaching 0 m/s

Question 37

Factors affecting thinking distance:

Answer 37

- tiredness - drugs/alcohol - distractions

Question 38

Factors affecting braking distance:

Answer 38

- speed - road conditions - vehicle conditions

Question 39

Describe how you investigate how mass affects acceleration

Answer 39

- set up the ramp on the lowest setting - attach a piece of card on to the top of the trolley - find the mass of the trolley - fasten the pulley to the end of the bench and set up the string - set up 2 light gates - one near the top and one near the bottom of the ramp - put a mass at the end of the string - release the trolley from the top of the ramp and record the speed as it passes through each light gate (using a data logger) - repeat adding 100g mass each time

Question 40

What is the relationship between mass and acceleration?

Answer 40

when mass increases, acceleration decreases (inversely proportional)

Question 41

Describe how you would investigate how force affects acceleration

Answer 41

- set up the ramp, attach a piece of card to the top of the trolley, find the mass of the trolley - fasten the pulley to the end of the bench and set up the string, set up 2 light gates at the top and bottom of the ramp - add 5 masses to the mass holder on the end of the string - release the trolley and record the time passing through each light gate - remove one mass from the stack and add it to the top of the trolley (will keep the total mass constant) - repeat for each further mass on the stack

Question 42

What is the relationship between force and acceleration?

Answer 42

as force increases, acceleration increases (directly proportional)

Question 43

Define inertial mass

Answer 43

the ratio of force to acceleration

Question 44

Define momentum

Answer 44

Momentum is a quantity of a moving body that is proportional to its mass and velocity - how difficult the object is to stop

Question 45

What is conservation of momentum?

Answer 45

In a closed system, the total momentum before an event is the same as after the event.

Question 46

Why are cars designed to slow people down over a longer period of time?

Answer 46

- a longer time means a smaller resultant force because there's a reduced rate of change of momentum - this means the force is smaller so less chance of injury