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Physics > Forces 1 new version > Flashcards

Forces 1 new version Flashcards

1
Q

What is the difference between scalar and vector quantities?

A

Scalar quantities have magnitude only, whereas vector quantities have both magnitude and an associated direction.

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2
Q

How might we represent a vector quantity?

A

With an arrow.

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3
Q

When representing vector quantities with an arrow, what does the length of the arrow represent?

A

The magnitude.

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4
Q

When representing vector quantities with an arrow, what does the direction of the arrow represent?

A

The direction of the vector quantity.

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5
Q

List some vector quantities

A

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

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6
Q

List some scalar quantities

A

-speed
-distance
-time
-length
-mass
-power
-temperature

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7
Q

What is a force?

A

A push or pull that acts on an object due to the interaction with another object.

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8
Q

What are the two types of forces between objects?

A

Contact and non-contact

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9
Q

What is the difference between a contact and non-contact force?

A

Contact - the objects interacting are physically touching.

Non-contact - the objects interacting are physically separated.

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10
Q

Examples of non-contact forces (hint: there are only three!)

A

-gravitational force

-magnetic force

-electrostatic force

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11
Q

Examples of contact forces

A

-friction
-air resistance
-normal contact force
-tension (pulling force through a rope)

(-water resistance)
(-lift)

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12
Q

Is force a vector or scalar quantity?

A

Vector.

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13
Q

Give examples to describe the interaction between pairs of objects which exert a force on each other.

A

The force of a ground on a box and the force of a box on the ground.

The force of an object on a surface and the force of the surface on the object.

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14
Q

Weight

A

The force acting on an object due to gravity.

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15
Q

What does the gravitational field around the Earth cause?

A

The force of gravity close to the Earth.

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16
Q

What two things does the weight of an object depend on?

A

-The gravitational field strength at the point where the object is

-The mass of the object

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17
Q

What is the formula for weight?

A

W = mg

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18
Q

What is the unit for weight?

A

Newtons, N

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19
Q

What is the unit for mass, m?

A

kg

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20
Q

What is the unit for gravitational field strength, (g)?

A

N/kg

or m/s²

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21
Q

Centre of mass

A

A single point through which the weight of an object may be considered to act.

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22
Q

Describe the relationship between the weight and mass of an object.

A

Directly proportional.

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23
Q

How can we measure the weight of an object?

A

Using a calibrated spring-balance (a newtonmeter).

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24
Q

If the distance between two objects were to increase, what would happen to the strength of a non-contact force between them?

A

It would decrease.

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25
Q

How can we find the centre of mass of an irregular object?

A

By hanging a plumb line from a bung between the arms of a clamp on a clamp stand.

Draw crosses where the plumb line falls on the object.

Repeat hanging the object (we used whiteboards) from different points.

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26
Q

A gravitational force is always what?

A

Attractive
Acting between all masses

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27
Q

Magnetic force

A

-Acts between magnetic poles
-Unlike poles attract and like poles repel

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28
Q

Electrostatic force

A

-Between + and - charges
-Unlike charges attract and like charges repel

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29
Q

How can the interaction between pairs of objects which exert a force on each other be represented?

A

as vectors

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30
Q

What is displacement as a vector quantity?

A

It gives the distance travelled and in what direction, for example travelling 50 miles East.

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31
Q

Reaction force

A

Force exerted in the opposite direction to an action (original )force.

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32
Q

Normal contact force

A

The reaction force experienced by an object at rest on a surface.

This reaction force is at 90° to the surface, acting upwards in opposition to the weight of an object.

(For example, a box on a table).

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33
Q

Tension force

A

A pulling force exerted by each end of an object such as a string or rope when it is being stretched.

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34
Q

Friction force

A

A force that acts in opposition to the pushing force that is trying to change an object’s motion.

It always acts to slow a moving object down.

It converts kinetic energy into heat.

(two objects sliding past each other experience this force e.g. a box sliding down a slope).

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35
Q

Air resistance

A

A force of friction produced when an object moves through the air.

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36
Q

What is another name for the normal contact force?

A

-Reaction force
-Normal reaction force
-Normal force

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37
Q

Resultant force

A

A single force that describes all of the forces acting on a body.

38
Q

How do we calculate the resultant of two forces that act in a straight line? (so from a scaled vector diagram?)

A

-Work out the difference in the two forces.

39
Q

If a car has more force (N) acting on the way it is facing than backwards, what is the car doing?

A

Accelerating

40
Q

If a car has equal force (N) acting on the way it is facing as backwards, what is the car doing?

A

Moving at a constant velocity
or
Is stationary

41
Q

Speed vs Velocity

A

Speed - only has magnitude
Velocity - has both magnitude and direction

42
Q

If a car has more force (N) acting backwards than the way it is facing, what is the car doing?

A

Decelerating

43
Q

When describing resultant forces we must …

A

state the resultant force

-state in which direction the force is acting

-to get e.g. 25N to the left

44
Q

When would we say an object is in a state of equilibrium?

A

When all the forces that act upon the object are balanced i.e. the resultant force is zero.

45
Q

A cyclist pushes on his pedals moving north with a force of 30N against a wind pushing him east with a force of 40N.

Calculate the resultant force and his direction.

A

-use a vector diagram
-find a scale factor (e.g. 1cm = 10N)

-in this case, draw a line with an arrow pointing north (3cm)

-from the TOP of this line draw another arrow pointing east (4cm)

-turn this into a triangle and measure the line (5cm)

-use Pythagoras to check your answer

-scale back up and state the direction

46
Q

How would we find the bearing from a vector diagram?

A

-Draw an angle in a clockwise direction from the (north) facing line to the one you drew (inside the triangle)

-Use a protractor to measure the angle

47
Q

Bike man is an example of what?

A

How a single force can be resolved into two components acting at right angles to each other.

The two component forces together have the same effect as the single force.

48
Q

What is the equation for resultant force?

A

mass x acceleration

49
Q

What is the equation for acceleration

A

a = ∑force ÷ mass

50
Q

What are free body diagrams?

A

Diagrams showing all the forces acting on an object using force arrows.

They can be used to describe qualitatively how several forces lead to a resultant force on an object.

This includes balanced forces when the resultant force is zero.

Picture the Cognito plane neowww

51
Q

What is the gravitational field strength of the Earth?

A

9.8 N/kg

52
Q

What is the gravitational field strength of the moon?

A

1.6 N/kg

53
Q

What is the gravitational field strength of the Jupiter and Mars?

A

Jupiter - 26

Mars - 3.75

54
Q

When using vector diagrams, how might we CALCULATE an angle? (rather than just measuring it with a protractor)

A

Using trigonometry

55
Q

If the angle of a resultant force is below the horizontal, what must we do?

A

-Measure from the horizontal to the drawn line

-See what angle is the same in the triangle

-Use trig

-Change answer to a minus

56
Q

Instead of saying e.g. ‘North West’ what is fancier/more appropriate for calculations?

A

e.g. 67.4° to the horizontal, acting left.

57
Q

What words can you use when describing the motion of an object?

A

-Accelerating
-Decelerating
-Upwards
-Downwards
-To the left
-To the right
-Stationary/accelerating at a constant velocity

58
Q

How to tell which force is resultant?

A

Not one of the main two forces arranged tip-to-tail.

59
Q

Give examples of the forces involved in stretching an object.

A

Stretching requires two forces of tension, acting away from each other.

60
Q

Explain why, to change the shape of a stationary object (by stretching, bending or compressing), more than one force has to be applied.

A

If only one force acts on an object the object will accelerate/ rotate instead of deforming.

61
Q

Describe the difference between elastic deformation and inelastic deformation caused by stretching forces.

A

Elastic deformation means that a material will return to its original shape when the deforming force is removed.

Inelastic deformation means that the material will not return to its original shape when the deforming force is removed. (exceeding limit of proportionality?)

62
Q

What is the unit for force, F?

A

N (newtons)

63
Q

What is the symbol for spring constant?

A

k

64
Q

What is the unit for spring constant?

A

N/m

65
Q

What is the unit for extension, e?

A

metres, m

66
Q

What is the equation that describes linear elastic deformation?

A

F = k e

Force = spring constant x extension

67
Q

Describe the difference between a linear and non-linear relationship between force and extension. (using the example of a spring)

A

For a linear relationship, the extension is directly proportional to the force applied, so the spring exhibits elastic deformation.

After the limit of proportionality is exceeded (shown as a point on a graph- which you can label P btw) the relationship is no longer linear. This means that for forces applied, the spring will not return to its original shape - exhibiting inelastic deformation.

68
Q

How do you calculate a spring constant? (in linear cases)

A

Rearrange F = k e

or Ee = 1/2 k e²

69
Q

How do you calculate work done in stretching (or compressing) a spring (up to the limit of proportionality)?

A

using the equation:

Ee = 1/2 k e²

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

Because Ee is equal to Work done

70
Q

Give examples of the forces involved in bending an object.

A

Bending requires two forces, one acting clockwise and one acting anticlockwise (pick up ya ruler and try).

71
Q

Give examples of the forces involved in compressing an object.

A

Compression involves two equal forces acting towards each other.

72
Q

Describe the relationship between the extension of an elastic object, such as a spring, and the force applied.

A

The extension is directly proportional to the force applied, provided that the limit of proportionality is not exceeded.

73
Q

Provided a spring is not ___________deformed, the ____ ____on the spring and the _______ _________ ______ stored are equal.

A

inelastically
work done elastic potential energy

74
Q

What goes on the axis of a force - extension graph?

A

-Extension (m) on the x-axis

-Force (N) on the y-axis

75
Q

What is meant by ‘deformation’

A

The change in shape of an object as a result of forces being applied to it.

76
Q

Extension

A

The increase in length of a spring when it’s stretched (caused by a weight added)

77
Q

Why doesn’t a spring fall down when the force acting on it is increased e.g. by adding more mass?

A

The solid support exerts an equal and opposite force upwards.

78
Q

What is Hooke’s law?

A

F = k e

i.e. the directly proportional relationship between the extension of an elastic object, such as a spring, and the force applied.

79
Q

What does a force that stretches (or compresses) a spring do?

A

Work

80
Q

What is stored in a spring?

A

Elastic potential energy.

81
Q

What does applying multiple forces to an object cause it to do?

A

Compress, Stretch, or Bend

82
Q

Spring constant

A

An object’s spring constant is a measure of how many Newtons of force it would require to stretch (or compress) the object by 1 metre.

You can think of it as a measure of how stiff the object is. Objects with a higher spring constant are more stiff, so they require more force to stretch.

83
Q

What does a lower spring constant mean?

A

An object is more elastic/less firm so easier to stretch.

84
Q

When a spring is stretched, energy is transferred to its ________ _____ energy store.

Then when the spring is released, most of that energy is transferred to _______ energy.

A

elastic potential
kinetic

85
Q

What is the formula for elastic potential energy?

A

Ee = 1/2 k e²

86
Q

Another way of saying limit of proportionality?

A

Elastic limit.

87
Q

What is extension?

A

The increase in the length of a spring when it’s stretched

or

The decrease in length of a spring when it’s compressed

88
Q

What does the gradient of a force-extension graph tell you?

A

The value of the spring constant, k (when linear)

89
Q

What does the area beneath the straight line on a force-extension graph tell you?

A

The energy transferred to the spring/ the elastic potential energy.

90
Q

What is elastic potential energy?

A

The energy transferred to an object as it’s stretched.

Physics (11 decks)

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