Forces

Question 1

Scalar

Answer 1

Magnitude only

Question 2

Vector

Answer 2

Magnitude and direction

Question 3

Examples of contact forces

Answer 3

Friction, air resistance, tension

Question 4

Examples of non-contact forces

Answer 4

Gravitational force, electrostatic force and magnetic force

Question 5

Weight

Answer 5

The force acting on an object due to gravity

Question 6

How is weight measured

Answer 6

Newtonmeter

Question 7

Why must more than one force be applied to compress, bend or stretch and object

Answer 7

Because if there was only one force acting in the object, it would accelerate in the direction of that force

Question 8

Elastic deformation

Answer 8

When an object is deformed and returns back to its original shape once forces are removed

Question 9

Inelastic deformation

Answer 9

When an object is deformed and doesn’t return to its original shape when forces are removed

Question 10

Hooke’s Law

Answer 10

The extension of an elastic object, like a spring, is directly proportional to the force applied, provided that the limit of proportionality is not exceeded

Question 11

Moment

Answer 11

Turning effect of a force

Question 12

How does rotation occur

Answer 12

When forces are applied at a distance from the centre of mass

Question 13

If an object is balanced..

Answer 13

The total clockwise moment = the total anticlockwise moment

Question 14

Levers

Answer 14

Used to apple force to an object, by using a smaller force applied at one end of the lever to generate a larger force at the other end

Question 15

Gears

Answer 15

Used to change the speed of direction of rotation

Question 16

What happens to the density of the atmosphere with increasing altitude

Answer 16

The atmosphere becomes less dense

Question 17

Explain why atmospheric pressure decreases with an increase in height

Answer 17

• pressure is created by collisions of air molecules
• the quantities of molecules (weight) decreases as the height increases
• this means atmospheric pressure decreases with increased height

Question 18

How does pressure in fluids increase with depth

Answer 18

• As the depth increases, the mass of liquid above that depth also increases
• This means that the force due to the mass increases
• since the force has increased whilst the area remained constant, the pressure will increase

Question 19

Why does pressure in fluids increase with density

Answer 19

• as the density of a fluid increases, the number of particles in a given volume increases
• so the weight of the fluid is greater
• this means that the force from the fluid above a certain point is large
• since the force has increased, so has the pressure

Question 20

Why are objects in a fluid subject to upthrust

Answer 20

• when an object is submerged in a fluid, it has a higher pressure below it than it does above as there is more weight at the bottom than at the top
• this leads to upthrust

Question 21

What is upthrust always equal to

Answer 21

The weight of fluid that the object displaces

Question 22

What factors influence whether an object will sink or float

Answer 22

• upthrust
• weight
• density

Question 23

Explain why an object with a density greater than water can never float

Answer 23

• upthrust is equal to the weight of the displaced fluid
• if the density of the object is high, there wouldn’t be enough volume displaced to produce an upthrust larger than the objects weight
• this means it will sink

Question 24

Atmosphere

Answer 24

A thin layer of air round the Earth

Question 25

Scalar quantities

Answer 25

- mass - time - speed - volume - temperature - density

Question 26

Vector quantities

Answer 26

- displacement - velocity - acceleration - momentum - force - weight

Question 27

Typical values for walking, running and cycling

Answer 27

Walking = ~1.5 m/s Running = ~3 m/s Cycling = ~6 m/s

Question 28

Velocity

Answer 28

Speed in a given direction

Question 29

Why does motion in a circle involve constant speed but changing velocity

Answer 29

Because velocity is a vector quantity that depends on speed and direction

Question 30

How to calculate speed of an object from a distance-time graph

Answer 30

The gradient

Question 31

Terminal velocity

Answer 31

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

Question 32

Explain what happens when a skydiver jumps out of a plane

Answer 32

- initially the air resistance is small as the skydiver isn’t falling very quickly - as they speed up (accelerate), the air resistance increases, eventually growing large enough to balance the downwards weight force - once air resistance equals weight, the resultant force is 0 - they’re not travelling at a constant speed (terminal velocity) -

Question 33

Explain what happens when the skydiver opens a parachute

Answer 33

- when the parachute opens there is a large upward force which causes the person to decelerate - eventually the forces balance again and the person reaches a new much slower terminal velocity

Question 34

Newton’s first law

Answer 34

If the resultant force acting on an object is 0 and: - the object is stationary, the object remains stationary - the object is moving, the object continues to move at a constant speed

Question 35

Inertia

Answer 35

The tendency of an object if at rest to continue in its state of rest, or if moving at a constant velocity to stay at a constant velocity

Question 36

Relationship between acceleration and inertial mass

Answer 36

Inversely proportional Greater inertial mass = small acceleration Smaller inertial mass = large acceleration

Question 37

Newtons Secind slaw

Answer 37

F=ma

Question 38

Newton’s third law

Answer 38

Whenever 2 objects interact, they exert equal and opposite force on each other

Question 39

Stopping distance

Answer 39

The sum of the distance the vehicle travels during drivers reaction time (thinking distance) and the distance it travels under the braking force (braking distance)

Question 40

What affects reaction time

Answer 40

- tiredness - drugs - alcohol - distractions

Question 41

What affects braking distance

Answer 41

- road and weather conditions (icy, wet) - condition of vehicle (brakes, tyres)

Question 42

Explain what happens to speed when brakes are applied

Answer 42

When a force is applied to the brakes of a vehicle, work done by the friction force of the brakes and wheels reduces the kinetic energy of the vehicle and temperature increases

Question 43

Relationship between braking and deceleration

Answer 43

The greater the breaking force the greater the deceleration

Question 44

Dangers of large decelerations

Answer 44

Brakes overheating or loss of control

Question 45

Momentum

Answer 45

Total momentum before an event = total momentum after the event

Question 46

Safety features of cars

Answer 46

- air bags - seatbelts - crumple zones