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GCSE Physics > P2 - Forces > Flashcards

P2 - Forces Flashcards

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1
Q

What are the differences between a scalar and vector quantity?

A
  • Scalar only has magnitude (size)

- Vector has magnitude and direction, eg forces (can be represented by arrows)

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2
Q

What are the differences between contact and non contact forces?

A
  • Contact: objects are touching ( friction, drag, tension, up thrust)
  • Non-contact: objects aren’t touching (gravity, electrostatic, magnetic)
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3
Q

What is gravity?

A
  • force of attraction between all masses

- force of gravity close to earth is due to gravitational field around planet

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4
Q

What is the difference between mass and weight?

A
  • Mass is the amount of matter an object contains and is constant
  • Weight is the force acting on an object due to gravity, changes in different gravitational fields
  • weigh and mass are directly proportional
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5
Q

What is a resultant force?

A

When more than one force acts on an object, it is a single force that is the overall result of all the other forces acting on the object

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6
Q

How is energy transferred when work is done on an object?

A

When work is done in a system, energy transfers take place eg work done to overcome friction increases heat energy

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7
Q

Describe what happens in terms of work done when overcoming forces

A

Overcoming forces requires energy
When a force moves an object, work is done on the object
This movement is called displacement

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8
Q

What is the difference between elastic and inelastic deformation?

A

Elastic deformation - will return to original shape once forces of compression, stretching or bending are removed (this requires more than one forces and must be balanced)

Inelastic deformation - do not return to original shape once forces are removed

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9
Q

What is a moment?

A

turning effect of a force, must be perpendicular

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10
Q

Describe a balanced moment (eg a seesaw)

A

Anti clockwise moment = clockwise moment

force x distance = force x distance

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11
Q

Why do some objects topple?

A
  • Weight acts directly down from centre of mass due to gravity
  • When the surface or object is tilted, the line of action of the weight (pointing down from centre of mass) will lie outside of the base of the object
  • unbalanced / resultant moment acting on block so it topples
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12
Q

Explain how levers and gears transmits the turning effects of a force

A
  • transmit turning effect (moment) of a force

- magnify size of force or distance force moves over

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13
Q

Describe pressure in a fluid

A
  • fluid = liquid or gas
  • particles move in fluid and collide with objects in fluid or surface of container
  • create a force normal (right angle) to surface
  • creates pressure
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14
Q

Explain why atmospheric pressure decreases as altitude increases

A
  • greater the altitude, less dense the atmosphere and lower the atmospheric pressure
  • at high altitudes, there is less air above a surface than at lower altitudes
  • less weight of air acting on the same surface (pressure = force / area would result in lower pressure outcome)
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15
Q

What does pressure in a column of liquid depend on?

A
  • height of column above the point

- density of liquid

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16
Q

The higher the column and more dense the liquid…

weight, force, pressure

A
  • greater weight above the point
  • greater force on the surface at that point
  • greater pressure
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17
Q

How does density effect pressure exerted?

A

The deeper an object is submerged the greater the pressure

So a more dense liquid exerts a greater pressure

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18
Q

Define upthrust

A

upwards force exerted by a fluid on a submerged object

greater height of liquid above bottom surface than top surface

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19
Q

What happens in terms of upthrust when an object floats?

A

weight = upthrust (not effected by density)

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20
Q

What happens when an object is less dense than a liquid?

A
  • displace a volume of liquid greater than its own weight
  • rises to surface
  • floats with some object remaining below surface
  • liquid displaced = weight of object
  • the lower the density the more of the object stays above surface
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21
Q

What happens when an object sinks?

A
  • denser than surrounding liquid

- can’t shaped enough liquid to equal own weight

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22
Q

What is the difference between distance and displacement?

A
  • distance is scalar
    how far an object moves, doesn’t take in to account direction of object or if it ends up back where it started
  • displacement is vector
    it has magnitude, which describes how far object has travelled from origin
    it has direction (direction of the straight line between start and end)
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23
Q

What variables effect speed?

A

age, fitness, terrain, distance

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24
Q

When travelling in a straight line, what is an objects velocity?

A

in a straight line, an object has constant speed and velocity

25
Q

What happens to speed and velocity when an object isn’t travelling in a straight line (eg round a corner)

A
  • speed can still be constant as it is scalar

- velocity changes because direction has changed (its is a vector that takes direction in to account)

26
Q

What happens to velocity and acceleration when an object is travelling in a circle?

A
  • constantly changing direction so constantly changing velocity
  • it is accelerating even if speed is constant
    (eg orbiting planets where gravity makes the object accelerate)
27
Q

What is Newton’s first law?

A

an object will remain in the same state of motion unless acted on by an external force

28
Q

When resultant force acting on an object is 0, what happens?

A
  • if object is stationary, it will remain stationary

- if object is moving it will continue to move at the same speed and same direction (constant velocity)

29
Q

What is the tendency for objects to continue in the same state of motion called?

A

inertia

30
Q

What causes velocity to change? (speed or direction)

A

external force acting

31
Q

When a car is travelling at a steady speed, what balances the driving forces?

A

resistive forces (eg friction)

32
Q

How is speed found on a distance-time graph?

A

gradient

33
Q

How is a stationary line show on a distance time graph?

A

Horizontal line

34
Q

In a d-t graph, the faster the speed…

A

steeper the gradient

35
Q

What does a distance time graph looking like when an object is accelerating?

A

curved line

36
Q

How is speed of an accelerating curve found?

A

at a particular time, a tangent can be drawn and gradient calculated

37
Q

Define acceleration

A

how quickly an object speeds up, slows down or changes direction

38
Q

What does the gradient of a velocity time graph show?

A

acceleration

39
Q

What is Newton’s second law?

A

acceleration of an object is proportional to resultant force acting on an object
and inversely proportional to mass of object

40
Q

Define mass

A
  • measure of inertia
  • describes how difficult it is to change velocity (m=f/a)
  • larger mass, bigger force needed to change velocity
41
Q

Explain terminal velocity in a fluid

A
  • object accelerates due to force of gravity
  • as it speeds up, resistance increases
  • result force reaches 0 when resistance and gravity are balanced
  • object falling at steady speed = terminal velocity
42
Q

What is the accelerating due to gravity near Earth’s surface?

A

10m/s2

43
Q

Explain the forces acting on a skydiver as it falls through the air

A
  • skydiver accelerates due to force of gravity
  • skydiver experiences frictional forces
  • weight is greater than resistance so skydiver continues to accelerate
  • speed and resistance increase as acceleration decreases
  • when resistance = weight and resultant forces =0, skydiver falls at terminal velocity
44
Q

How is terminal velocity represented in a velocity time graph?

A

speed gradient
curves as resistance increases but still accelerating
levels off at terminal velocity before parachute opens

45
Q

Explain Newton’s third law

A

for every action there is an equal and opposite reaction

  • when one object exerts a force on another, the other object exerts a force back
  • reaction force is of same type and equal in size, but opposite direction
46
Q

When does a change in momentum occur?

A
  • All moving objects have momentum

- when an unbalanced force acts on a object that is moving or unable to move, momentum changes

47
Q

What is momentum?

A

product of mass and velocity

force is the rate of change of momentum

48
Q

Explain why momentum should be considered in safety devices?

A
  • safety devices reduce force by increasing time over which change of momentum takes place
    e. g - gym crash mats cushion fall impacts increasing time it takes for someone to come to rest when they fall on to the floor
49
Q

How is momentum conserved in a closed system?

A

total momentum before an event = total momentum after event

can be seen in collisions

50
Q

What does a vehicles stopping distance depend on?

A
  • thinking distance (distance travelled during reaction time)
  • braking distance (distance travelled under braking force)
51
Q

What is the typical human reaction time?

A
  1. 2-0.9s

- a car travelling at 30m/s will travel 12-27m before braking starts

52
Q

Which factors can effect reaction time?

A

tiredness, drugs, alcohol, distraction (eg phone)

53
Q

How can reaction time be measured?

A
  • use light or sound signal and time how long it takes for someone to react
  • in a classroom - drop ruler vertically and catch as it falls - distance ruler drops can be used to calculate reaction time
54
Q

What factors can effect braking distance?

A

road conditions, vehicle conditions (worn breaks and tyres, over and under inflated tyres) and weather (wet, icy, snowy roads)

55
Q

How to brakes stop a vehicle?

A

apply force to the wheels

56
Q

The greater the braking force…

A

greater the deceleration of the vehicle

57
Q

Why does brake temperature increases during braking?

A
  • work done by frictional force

- transfers kinetic energy of vehicle in to heat energy

58
Q

What happens when braking force is too large?

A
  • brakes overheat
  • tyres loose traction which leads to skidding
  • more likely if brakes or tyres are in poor condition
59
Q

For a given braking distance, what happens when

a) mass is doubled
b) speed is doubled

A
  • doubling speed doubles force required

- doubling speed quadruples force required

GCSE Physics (11 decks)

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