P5 Flashcards

1
Q

What is the difference between a scalar and vector quantity?

A

Scalar quantities - magnitude only
Vector quantities - have magnitude and direction

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2
Q

How can a vector quantity be represented?

A

using an arrow

  • the length=magnitude
  • the direction of the arrow= direction of the vector quantity
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3
Q

What is a force?

A

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

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4
Q

What are contact forces?

A

The objects are physically touching

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5
Q

What are non-contact forces?

A

The objects are physically separated

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6
Q

Give examples of contact forces

A
  • friction
  • tension
  • air resistance
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7
Q

Give examples of non-contact forces?

A
  • gravity
  • electrostatic force
  • magnetic force
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8
Q

What is an interaction pair?

A

A pair of forces that are equal (in magnitude) and opposite in direction

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9
Q

Is force a scalar or vector quantity?

A

Vector

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10
Q

What is weight?

A

The force acting on an object due to gravity

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11
Q

How can you calculate the weight of an object

A

W= m x g

W= weight (N)
m= mass (kg)
g= gravitational field strength (N/kg)

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12
Q

Where does the weight of an object act?

A

at the object’s ‘centre of mass’

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13
Q

What is weight measured with?

A

a newton meter

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14
Q

Describe the relationship between the weight and mass of an object

A

the weight of an object is directly proportional to the mass of an object

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15
Q

What is the resultant force?

A

a number of forces acting on an object that may be replaced by a single force that has the same effect

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16
Q

What happens when the forces acting on an object combine to give a resultant force of 0?

A

The forces are balanced and the object is in equilibrium

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17
Q

When is work done on an object?

A

When a force causes an object to move through a distance (when the force causes a displacement of the object)

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18
Q

How can you calculate the work done by a force on an object?

A

W= F x s

W= work done (J)
F= force (N)
s= distance (m)

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19
Q

What happens when work is done against the frictional forces acting on an object?

A

It causes a rise in the temperature of the object

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20
Q

Why does more than one force have to be applied in order to change the shape of an object (by bending, stretching or compressing) ?

A

Otherwise the object (e.g. the string) would just move in the direction of the single applied force.

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21
Q

What is the difference between elastic deformation and inelastic deformation?

A

elastically deformed - if it can go back to its original shape and length after the force has been removed
- e.g. a spring, rubber band

inelastically deformed - if it does not return to its original shape and length after the force has been removed, its shape will have been changed permanently

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22
Q

Describe the extension of an elastic object

A

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

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23
Q

What is the equation for force?

A

F= k x e

F= force (N)
k= spring constant (N/m)
e= extension (m)

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24
Q

What does a force that stretches or compress a spring do?

A

It does work and elastic potential energy is stored in the spring

provided the spring is not inelastically deformed, the work done and the elastic potential energy stored are equal

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25
Q

What is the equation used to calculate elastic potential energy (up to the limit of proportionality)?

A

Ee = 1/2 x k x e^2

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26
Q

What is a moment?

A

The turning effect of a force

27
Q

How do you calculate the size of the moment?

A

M = F x d

M= moment (Nm)
F= force (N)
d= perpendicular distance from the pivot to the line of action of the force (m)

28
Q

What is the role of a lever?

A

Levers increases the distance from the pivot at which the force is applied

this means less force is needed to get the same movement

29
Q

Explain the function of gears

A

Gears are used to transmit the rotational effect of a force from one place to another

  • their teeth interlock that when one turns another turns in the opposite direction
  • the larger gear moves slower
30
Q

Explain what happens when an object is balanced

A

The total clockwise moment about a pivot equals the total anticlockwise moment about that pivot

31
Q

Describe the pressure in fluids (liquids/gases)

A

The pressure in fluids causes a force normal (at right angles) to any surface

32
Q

What equation can be used to calculate the pressure at the surface of a fluid?

A

p= F/A

p= pressure (Pa)
F= force normal to a surface(N)
A= area of that surface (m^2)

33
Q

How can you calculate the pressure due to a column of liquid?

A

pressure = height x density x gravitational field strength

p= h x p x g

p= pressure (Pa)
h= height (m)
p= density (kg/m^3)
g= gravitational field (N/kg)

34
Q

Why (in a liquid) does pressure at a point increase with the height of liquid above that point and with the density of the liquid?

A

The pressure increases because there are more water particles on top of the point and the increased pressure is due to the weight of the water above

35
Q

What does a partially or submerged object experience?

A

upthrust- a greater pressure on the bottom surface than on the top surface which creates a resultant force upwards

36
Q

Why do objects weigh less when in fluids?

A

The weight of an object decreases as the object experiences upthrust when submerged in a fluid. The resultant force of the weight and upthrust gives a reduced weight

37
Q

What does Archimedes principle state?

A

When a body is partly or totally immersed in a fluid, there is an upthrust that is equal to the weight of fluid displaced

38
Q

What is the atmosphere?

A

a thin layer of air around the Earth
(it gets less dense with increasing altitude)

39
Q

What creates atmospheric pressure?

A

Air molecules colliding with a surface

40
Q

What happens to the number of air molecules above a surface as the height of the surface above ground level increases?

A

The number of air molecules decreases

41
Q

What happens as height increases?

A

atmospheric pressure decreases

42
Q

True or False: Distance is a vector quantity?

A

False- distance is scalar

43
Q

What is displacement?

A

This includes both the distance an object moves (from start point to finish point) and the direction of the straight line

44
Q

What type of quantity is speed?

A

Speed is scalar

45
Q

Give typical values for the speed of walking running and cycling

A
  • walking - 1.5 m/s
  • running- 3 m/s
  • cycling- 6 m/s
46
Q

What is a typical value for the speed of sound in air?

A

330 m/s

47
Q

How can you calculate the distance travelled in a specific time ( at a constant speed)?

A

s= v x t

s= distance (m)
v= speed (m/s)
t= time (s)

48
Q

What is velocity?

A

The speed of an object in a given direction
- so it is a vector quantity

49
Q

What is meant by terminal velocity?

A

after a while, a falling object would have a constant velocity

50
Q

What is the equation for acceleration?

A

acceleration = change in velocity/ time taken

51
Q

Define inertia

A

The tendency of an object to continue in its current state of motion

52
Q

What is Newton’s first law?

A

If the resultant force acting on an object is 0:
- if it is stationary, it will remain stationary
- if it is moving, it will move at a constant speed

53
Q

What is Newton’s second law?

A

The resultant force acting on an object is directly proportional to the acceleration and indirectly proportional to the mass

F= ma

54
Q

What is Newton’s third law?

A

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

(Every action has an equal opposite reaction - Thomas Jefferson)

55
Q

What is momentum?

A

mass x velocity

56
Q

Describe the conservation of momentum principle

A

In a closed system, the momentum before an event is equal to the total momentum after

57
Q

What happens when a car crashes (into a brick wall)?

A
  • The momentum decreases to 0 almost immediately
  • the massive change in momentum means that anyone inside the car would experience a huge force
58
Q

What is meant by stopping distance?

A

The distance it takes a car to stop in an emergency

(thinking distance + braking distance)

59
Q

What is ‘thinking distance’?

A

The distance travelled between when the driver realises they need to brake and when they apply the brake

60
Q

What is ‘braking distance’?

A

The distance the car travels between the driver applying the brakes and the car coming to a stop

61
Q

Factors affecting thinking distance

A
  • drugs/alcohol
  • tiredness
  • distractions (e.g. mobile phone)
62
Q

factors affecting braking distance

A
  • road conditions
  • tire conditions
  • brakes conditions
  • initial car speed
63
Q

What are dangers of large decelerations?

A

the greater the braking force the greater the deceleration.

  • A larger deceleration can cause overheating/skidding
  • It will also transfer more stopping force to the passengers which would harm the passengers