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A SL Physics 2024/2025 > Topic A.2 Forces and Momentum > Flashcards

Topic A.2 Forces and Momentum Flashcards

1
Q

Resultant force

A

Sum of all the forces acting on an object

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2
Q

Resolving forces

A

A single force can be resolved (broken down) into two components at 90* to each other

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3
Q

Newton’s first law

A

An object continues in uniform motion in a straight line or at rest unless a resultant external forces acts

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4
Q

Newton’s second law

A

The resultant force on an object is proportional to the acceleration providing the mass of the object remains constant

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5
Q

Newton’s third law

A

For every action on an object there is an equal but opposite reaction on another object

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6
Q

Two types of forces

A

Contact and field

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7
Q

Contact forces

A

Requires objects to be in contact with each other

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8
Q

Contact forces example

A

Normal, friction, tension, elastic

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9
Q

Field forces example

A

Gravitational, electric, magnetic

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10
Q

Field force

A

Force that can act at a distance

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11
Q

Normal force

A

When an object pushes on a surface, surface pushes back on the object

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12
Q

Objects on an incline - normal force is calculated how?

A

Fn = mg

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13
Q

Components of the weight force are split up how in an object on the incline

A

Going down the slope is mgsin0, acting on an angle is mgcos0, weight is mg

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14
Q

Surface friction

A

Force that opposes motion on two solid objects

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15
Q

Static friction

A

When a force is applied to an object but the force is not large enough to move the object, static friction acts

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16
Q

What happens when static friction reaches a maximum value?

A

It becomes dynamic friction and the object starts moving

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17
Q

What is the magnitude of static friction equal to?

A

The magnitude of the applied force

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18
Q

What is the coefficient of friction value?

A

Ratio of two forces (Ff and Fn)

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19
Q

How to calculate coefficient of static friction?

A

tan0, when the block is about to move

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20
Q

What happens when the force applied to the object exceeds the maximum static friction force?

A

It becomes dynamic friction and the object is moving

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21
Q

Which is bigger, static or dynamic friction?

A

Dynamic friction

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22
Q

What is the maximum value for a coefficient of friction?

A

Usually 1.0

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23
Q

Viscous drag force

A

The force acting on a moving object due to the viscosity of the fluid which it is moving through

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24
Q

What does the size of the drag force depend on? (6 factors)

A

Shape, size, surface and cross section of object, viscosity of fluid, speed of object

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25
Q

Why can’t Stoke’s law be used on big objects?

A

Turbulent flow (laminar) occurs

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26
Q

What does an object need to be to calculate drag force?

A

A small smooth sphere

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27
Q

Buoyancy

A

Ability of a fluid to provide a vertical upward force on an object placed on or in it

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28
Q

What is the size of the buoyancy force equal to?

A

The weight of the fluid displaced

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29
Q

An object will sink until when

A

When it has displaced its own weight of fluid

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30
Q

If an object is floating, which two forces are balanced

A

Weight force and buoyancy force

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31
Q

When an object is falling through a fluid, three vertical forces act on it - which three

A

Weight down
Buoyancy upwards
Viscous drag upward

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32
Q

What are the two constant forces on an object falling through a fluid?

A

Weight force downward, buoyancy upwards

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33
Q

What is the changing force on an object falling through a fluid?

A

The viscous drag force will increase as the speed increases

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34
Q

What are the forces on an object falling through a fluid at terminal velocity?

A

Fb+Fd = Fg

35
Q

Tension force

A

A pulling force, may cause on object to stretch

36
Q

Magnitude of the restoring force is equal to what?

A

The extension of length

37
Q

Elastic restoring force (Fh)

A

The object will exert a restoring force to return the object to the equilibrium position

38
Q

Spring constant

A

K, value that represents the stiffness of the object. Larger the force, stiffer the object. (Nm-1)

39
Q

What direction does a restoring force act in?

A

Opposite direction to the extension

40
Q

Object behaving elastically

A

Returns to original position after being stretched

41
Q

Maximum extension

A

After it is stretched past this point, it will be permanently deformed. Elastic limit

42
Q

Force fields

A

Region of space where an object may experience a force due to a property such as mass or charge

43
Q

Gravitational force field

A

A region of space where an object experiences a force due to its mass

44
Q

g

A

Gravitational field strength, 9.8Nkg-1 at earth’s surface

45
Q

What can gravitational force also be referred to when on earth?

A

Weight force

46
Q

Free body diagram

A

A diagram that shows all the forces acting on an object

47
Q

Balanced forces

A

Object remains at rest or continues at constant speed in a straight line

48
Q

Unbalanced forces

A

Forces in opposite direction are unbalanced, accelerates in direction of greater force

49
Q

How heavy we feel depends on what force?

A

Normal force

50
Q

If an object is in equilibrium, the sum of all forces…

A

Will add to 0 so resultant forces are 0

51
Q

p

A

Linear momentum, Ns

52
Q

Linear momentum (p)

A

The product of mass and velocity of an object. It is a vector so has both magnitude and direction

53
Q

What happens when an impulse is applied to an object with constant linear momentum?

A

The change in p will be equal to the impulse.

54
Q

j

A

Impulse, Ns

55
Q

Why can’t Newton’s 2nd law be used sometimes?

A

It assumes mass is constant, if mass is changing use change in p/change in t

56
Q

How may an impulse be found without a formula?

A

Area under a force time graph

57
Q

Law of conservation of momentum

A

The total linear momentum of a system remains constant provided no resultant external force acts on the system

58
Q

What does the law of conservation of momentum allow us to determine?

A

The outcome of collisions and explosions

59
Q

What happens to total energy in collisions?

A

It is conserved

60
Q

Elastic collision

A

No kinetic energy is lost (occurs between subatomic particles)

61
Q

Inelastic collision

A

Kinetic energy is lost (converted to heat and sound)

62
Q

What happens to kinetic energy in an explosion and why?

A

It increases and comes from the energy source of the explosion ie chem pot or elastic pot

63
Q

What is angular velocity?

A

Angular displacement (angle) over time taken

64
Q

Angular velocity units and symbol

A

Symbol w, units rads-1

65
Q

Centripetal acceleration

A

Acceleration towards the centre of a circle

66
Q

Centripetal force

A

Unbalanced force that acts to create circular motion

67
Q

How to break down a resolving force?

A

Vertical is Fsin0 and horizontal is Fcos0

68
Q

Translational equilibrium

A

When a resultant force on an object is zero and it is not accelerating

69
Q

What is the magnitude of static friction equal to?

A

Magnitude of the applied force

70
Q

Density

A

Mass/volume

71
Q

Angular velocity formula

A

2 π f

72
Q

How can an object be moving at a constant speed in a circle but still be accelerating?

A

Acceleration is rate of change of velocity, direction of motion is constantly moving so velocity is constantly changing.

73
Q

Centripetal force formulas x2

A

F=mv^2/r and F=mw^2r

74
Q

What are the balances of the forces in horizontal circular motion?

A

Vertical forces are balanced, there is an unbalanced horizontal force to the centre of the circle

75
Q

Where does centripetal force come from in horizontal circular motion?

A

Friction between tyres and road

76
Q

Horizontal circular motion - what happens if the car travels at a speed where the friction force is not large enough to provide a centripetal force?

A

Car continues in a straight line at a tangent to the bend

77
Q

Where does centripetal force come from in banked corners?

A

The horizontal component of the normal force

78
Q

What forces can the normal force be resolved into on banked corners?

A

Vertical component - balances weight, horizontal component - provides centripetal force

79
Q

Two key differences between vertical and horizontal motion

A
  • Vertical motion speed is not constant
  • Vertical motion - size of normal force varies throughout the motion
80
Q

Forces acting at the top of a loop (vertical circular motion)

A

Fg+Fn=Fc

81
Q

Formula for minimum speed

A

v= √rg

82
Q

What would you feel if normal force was 0?

A

Weightless sensation

83
Q

Forces acting on the bottom of a loop (vertical circular motion)

A

Fn up, Fg down. Fc=Fn-Fg

84
Q

Kinetic energy in a vertical circular motion loop

A

Ek (bottom) must = Ek(top)+Ep(top)

A SL Physics 2024/2025 (5 decks)

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