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GCSE Physics > P5 - Forces > Flashcards

P5 - Forces Flashcards

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1
Q

Scalar quantities

A

Have magnitude only

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2
Q

Vector quantities

A

Have magnitude and an associated direction

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3
Q

How can a vector quantity be represented (2)

A

By an arrow:

• The length of the arrow represents the magnitude, the direction of the arrow and the direction of the vector quantity

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4
Q

Force (2)

A
  • Is a push or pull that acts on an object due to the interaction with another object
  • Is a vector quantity
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5
Q

Contact forces

A

The objects are physically touching

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6
Q

Non-contact forces

A

The objects are physically separated

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7
Q

Examples of contact forces (4)

A
  • Friction
  • Air resistance
  • Tension
  • Normal contact force
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8
Q

Examples of non-contact forces (3)

A
  • Gravitational force
  • Electrostatic force
  • Magnetic force
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9
Q

Describe the interaction between pairs of objects which produce a force on each object (2)

A
  • When two objects interact, there is a force produced on both objects
  • An interaction pair is a pair of forces that are equal and opposite and act on two interacting objects
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10
Q

Weight (2)

A
  • Is the force acting on an object due to gravity

* Depends on the gravitational field strength at the point where the object is

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11
Q

What is the force of gravity close to Earth due to

A

The gravitational field around the earth

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12
Q

Formula linking weight, gravitational field strength and mass

A

Weight (N) = mass (kg) x gravitational field strength (N/kg)

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13
Q

Centre of mass

A

The weight of an object may be considered to act at a single point

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14
Q

What is the relationship between weight of an object and mass of an object

A

They are directly proportional

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15
Q

How is weight measured

A

Using a calibrated spring-balance (a newtonmeter)

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16
Q

Resultant force

A

• A number of forces acting on an object

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17
Q

Requered practical - force and acceleration (3) method

A
  • The force is varied by moving spare 100 g masses from the trolley to the falling mass hanger - the total accelerating mass is kept constant
  • The datalogger measures the speed - by timing how long the interrupt card takes to pass through each light gate
  • It then divides the change in speed by time taken to calculate the acceleration
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18
Q

Requered practical - force and acceleration - safety

A

Care should be taken that the falling masses don’t land on anyone and that the speeding trolley doesn’t hit anyone

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19
Q

Requered practical - force and acceleration (7) equipment

A
  • Dynamic trolley
  • Datalogger
  • Ruler - acts as a runway
  • pulley
  • string
  • Light gates
  • Interrupt cards
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20
Q

Requered practical - force and acceleration - diagram

A

Chegg

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21
Q

Required practical - extension of a spring - method (6)

A
  • Ensure the ruler is vertical and aligned with top of the spring
  • Measure and record the length of the natural spring
  • Add 1N weights one at a time, up to 10 N measuring the spring’s length each time
  • Subtract the original length from the extended length to get the extension
  • Plot a graph - Force on y-axis and extension on the x-axis
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22
Q

Required practical - extension of a spring - Safety (3)

A
  • G-clamp the apparatus to the desk to prevent it from falling over
  • Keep it from under the mass
  • Wear safety glasses to protect eyes in case the spring snaps
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23
Q

How to calculate the resultant of two forces that act in a straight line (5)

A
  • Draw a scale drawing of the forces acting
  • Use a sensible scale (e,g 1cm = 1N)
  • Draw the resultant from the tail of the first arrow to the tip of the last arrow
  • Measure the length of the resultant with a ruler and use the scale to find the force in N
  • Use a protractor to measure the direction as a bearing
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24
Q

Examples of forces acting on an isolated object or system (2)

A
  • when a car travels at a constant speed, the driving force from the engine is balanced by resistive forces such as air resistance and friction in the car’s moving parts
  • an object falling at terminal velocity experiences the same air resistance as its weight
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25
Q

Equation for work done

A

Work done (J) = force (N) x distance (m)

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26
Q

What is work done

A

When a force moves an object through a distance, energy us transferred and work is done on the object

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27
Q

Describe the energy transfer when work is done

A

The force does ‘work’ to move the object and energy is transferred from one store to another

28
Q

Convert between newton-metres and joules

A

1 joule = 1 newton-metre

29
Q

What happens when work is done against frictional forces

A

It causes a rise in the temperature of the object

30
Q

Examples of forces used in stretching, bending or compressing an object (2)

A
  • Applied force

* Another force as well as the applied force

31
Q

Why does more than one force need to be applied to change the shape of a stationary object by stretching,bending or compressing

A

Otherwise the object would simply move in the direction of the applied force, instead of changing shape

32
Q

elastic deformation

A

An object has been elastically deformed if it can go back to it original shape and length after the force has been removed

33
Q

Inelastic deformation

A

An object has been inelastically deformed if it doesn’t return to its original shape and length after the force has been removed

34
Q

What is the relationship between an elastic object and the force applied

A

Directly proportional - provided that the limit of proportionality is not exceeded

35
Q

Equation linking force, spring constant and extension

A

Force (N) = spring constant (N/m) x extension (m)

36
Q

What is the linear relationship between force and extension

A

Directly proportional - so the gradient is equal to the spring constant

37
Q

What is the non-linear relationship between force and extension

A

The spring stretches more for each unit increase in force

38
Q

How to calculate work done in stretching a spring

A

Elastic potential energy = 0.5 x spring constant x (extension)2

39
Q

Distance (2)

A
  • Is how far an object moves

* Scalar quantity

40
Q

Displacement (2)

A
  • Includes both the distance an object moves, measured in a straight line from the start point to the finish point and the direction of the straight line
  • Vector quantity
41
Q

Speed

A
  • Does not involve direction

* Scalar quantity

42
Q

Typical values of speed for a person walking, running and cycling

A

Walking - 1.5 m/s
Running - 3 m/s
Cycling - 6 m/s

43
Q

Typical values of speed for cars, trains and planes

A

Car - 25m/s
Train - 30 m/s
Plane - 250 m/s

44
Q

Equation to calculate the distance travelled by an object moving at a constant speed

A

Distance travelled (m) = speed (m/s) x time (s)

45
Q

Velocity (2)

A
  • Is an objects speed in a given direction

* Vector quantity

46
Q

Objects moving in a circle

A

At a constant speed an object has a constant changing velocity, as the direction is always changing e.g a car at a roundabout

47
Q

Distance-time graphs (6)

A
  • Gradient = speed
  • Flat sections are where it’s stationary
  • Straight uphill sections mean its travelling at a steady speed
  • Curves represent acceleration or deceleration
  • A steepening curve means it speeding up (Increased gradient)
  • A levelling off curve means it’s slowing down
48
Q

Equation for acceleration

A

Acceleration (m/s2) = change in velocity (m/s)/time taken (s)

49
Q

Velocity-time graph (7)

A
  • Gradient = acceleration
  • Flat sections - travelling at steady speed
  • The steeper the graph, the greater the acceleration or deceleration
  • Uphill sections are acceleration
  • Downhill sections are deceleration
  • curves mean changing acceleration
  • The area under any section of the graph is equal to the distance travelled in that time
50
Q

What is the acceleration of an object falling freely near the earth’s atmosphere

A

9.8 m/s2

51
Q

An object falling through a fluid (2)

A
  • Initially accelerates due to the force of gravity

* Eventually the resultant force will be zero and the object will move at its terminal velocity

52
Q

Newton’s first law (3)

A

If the resultant force acting on an object is zero and:
• the object is stationary, the object remains stationary
• The object is moving, the object continues to move at the same speed and in the same direction, so the object continues to move at the same velocity

53
Q

Apply Newton’s First Law to explain the motion of objects with a uniform velocity

A

• when a vehicle travels at a steady speed the resistive force balance the driving force

54
Q

What is inertia?

A

Is the tendency of objects to continue n their state of rest or of uniform motion

55
Q

Newton’s second law

A

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

56
Q

Equation linking resultant force, mass and acceleration

A

Resultant force (N) = mass(kg) x acceleration (m/s2)

57
Q

What is inertial mass (2)

A
  • Is a measure of how difficult it is to change the velocity of an object
  • Is defined as the ration of force over acceleration (m=f/a)
58
Q

Newtons third law

A

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

59
Q

Apply newton’s third law to examples of equilibrium situations (3)

A
  • A man pushing a wall
  • As the man pushes the wall there is a normal contact force acting back on him - these two forces are the same
  • As the man applies a force and pushes the wall, the wall ‘pushes back’ on him with equal force
60
Q

What is stopping distance

A

Stooping distance = thinking distance + braking distance

61
Q

Typical ranges of reaction times

A

0.2s to 0.9s (vary from person to person)

62
Q

How can a driver’s reaction time be affected (4)

A
  • Tiredness
  • Drugs
  • Alcohol
  • Distractions
63
Q

Methods used to measure human reaction times (2)

A
  • Computer-based test - clicking a mouse when the screen changes colour
  • ruler drop test
64
Q

How can braking distance of a vehicle be affected (2)

A
  • By adverse road and weather conditions

* Poor condition of the vehicle

65
Q

Factors which affect the distance required for road transport vehicles to come to rest in emergencies (2)

A
  • thinking distance - (the time between the driver seeing a hazard and applying the brakes)
  • Braking distance - (is the distance taken to stop under the braking force)
66
Q

Typical braking distances (3)

A
  • 14m at 30mph
  • 55m at 60mph
  • 75m 70mph

GCSE Physics (7 decks)

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