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A-Level Physics > 5. Mechanics > Flashcards

5. Mechanics Flashcards

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1
Q

What are the two categories all quantities fall into?

A

scalar, vector

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2
Q

What is the difference between a scalar quantity and a vector quantity?

A

scalar quantities have magnitude only; vector quantities have magnitude and direction

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3
Q

State 7 scalar quantities

A
  • time
  • mass
  • temperature
  • distance
  • length
  • speed
  • energy
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4
Q

State 6 vector quantities

A
  • weight
  • acceleration
  • force
  • displacement
  • velocity
  • momentum
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5
Q

When is an object in equilibrium?

A

when there are no resultant forces and no resultant moments

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6
Q

What is a moment?

A

the force multiplied by the perpendicular distance from the pivot to the line of action of the force

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7
Q

What is the principle of moments?

A

if a system is in equilibrium, the sum of the clockwise moments = the sum of the anticlockwise moments, at any point

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8
Q

What is a couple?

A

a pair of forces of equal size which act parallel to each other but in opposite directions

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9
Q

What is the centre of mass?

A

the single point that you can consider all the weight to act through

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10
Q

What is displacement (s)?

A

distance and direction from starting point in a straight line

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11
Q

What is speed (v)?

A

how fast something is going regardless of direction

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12
Q

What is velocity (v)?

A

how fast something is going with direction

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13
Q

What is acceleration (a)?

A

the rate of change of velocity

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14
Q

What does the gradient of a displacement-time graph represent?

A

velocity

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15
Q

What does the gradient of a velocity-time graph represent?

A

acceleration

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16
Q

What does the area under a velocity-time graph represent?

A

change of displacement

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17
Q

What does the area under an acceleration-time graph represent?

A

change in velocity

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18
Q

What is Newton’s first law of motion?

A

if there are no resultant forces acting on a object it will either:

  • stay at rest
  • travel at a constant speed in a straight line (constant velocity)
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19
Q

What is Newton’s second law of motion?

A

“the acceleration of an object is proportional to the resultant force acting on it”

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20
Q

What is the equation representing Newton’s second law?

A

F = ma

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21
Q

What is Newton’s third law of motion?

A

“if object A exerts a force on object B, then object B exerts an equal but opposite force on object A”

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22
Q

How can you find the centre of mass of a flat object?

A
  • hang the object freely from a point
  • draw a vertical line downwards from the point of suspension
  • use a plumb bob to get the line exactly vertical
  • hang the object from several different points, and draw vertical lines
  • the centre of mass is where the line cross
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23
Q

When will can object topple over?

A

if the line of action of the objects weight falls outside its base area

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24
Q

What is freefall?

A

the motion of an object undergoing an acceleration of ‘g’

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25
Q

What is friction?

A
  • a force that opposes motion

- turns kinetic energy into thermal energy

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26
Q

What are the two main types of friction?

A
  • contact friction

- fluid friction

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27
Q

When does contact friction happen?

A

between solid surfaces

28
Q

What is fluid friction also known as?

A
  • drag
  • fluid resistance
  • air resistance
29
Q

What is fluid friction caused by?

A

a gas or a liquid

30
Q

What three factors affect drag?

A
  • viscosity of the fluid
  • speed
  • surface area of profile
31
Q

What is the relationship between drag and speed?

A

drag is directly proportional to speed squared

32
Q

What is lift?

A

an upwards force on an object moving through a fluid

33
Q

How does lift occur?

A

lift happens when the shape of an object causes the fluid flowing over it to change direction

34
Q

What direction does lift act in comparison to the direction of fluid flow?

A

perpendicular

35
Q

What direction does drag act in comparison to the direction of fluid flow?

A

parallel

36
Q

When does terminal velocity occur?

A

when the frictional forces on an object are equal to the driving forces on an object

37
Q

What are the two main ways of increasing a vehicle’s maximum speed?

A
  • increasing the driving force

- reducing the frictional force

38
Q

How are momentum, mass and velocity related?

A

momentum = mass x velocity

39
Q

Is momentum a scalar or vector quantity?

A

vector

40
Q

What is the principle of conservation of linear momentum?

A

the total momentum before a collision = the total momentum after a collision, provided no external forces act

41
Q

What is an elastic collision?

A

a collision where both momentum and kinetic energy are conserved

42
Q

What is an inelastic collision?

A

a collision where momentum is conserved but kinetic energy is not conserved

43
Q

Are most real life collisions elastic or inelastic?

A

inelastic

44
Q

What must be applied for a change in momentum to occur?

A

a force

45
Q

What is the relationship between force, change in momentum and time?

A

force = change in momentum / time

46
Q

What is impulse?

A

the product of force and time

47
Q

What is impulse equal to?

A

change in momentum

48
Q

What are the units of impulse?

A

Ns or kgms^-1

49
Q

What does the area under a force against time graph equal?

A
  • the impulse

- the change in momentum

50
Q

What three things in a car increase the duration of impact and hence decrease the size of the force when change in momentum is conserved?

A
  • crumple zones
  • seat belts
  • air bags
51
Q

How do crumple zones decrease the size of the force on a passenger?

A

deform plastically (permanently) on impact, causing the car to take longer to stop, increasing the impact time and decreasing the force on the passengers

52
Q

How do seat belts decrease the size of the force on the passenger?

A

stretch slightly, so they increase the impact time for the wearer, reducing the force acting on their chest

53
Q

How do air bags decrease the size of the force on the passenger?

A

slow down the passengers more gradually, and prevent them from hitting hard surfaces inside the car

54
Q

When is work done?

A

when energy is transferred

55
Q

What is the equation linking work done, force and distance?

A

work done = size of force in direction of travel x distance travelled

56
Q

How is work done calculated when the force and direction of travel aren’t parallel?

A

work done = force x cos(angle between force and direction of travel) x distance

57
Q

What is the area under a force against distance graph equal to?

A

work done

58
Q

What is power?

A

rate of doing work

59
Q

What are the units of power?

A

Watts

60
Q

How is power calculated?

A

power = change in work done / time

61
Q

What is the equation linking power, force and velocity?

A

power = force x velocity

62
Q

What is the principle of conservation of energy?

A
  • energy cannot be created or destroyed
  • it can only be transferred from one form to another
  • but the total amount of energy in a closed system will not change
63
Q

What is efficiency?

A

a way to quantity how much of the energy (or power) put in is transferred into useful energy (or power)

64
Q

How is efficiency calculated?

A

efficiency = ((useful energy/power out) / (total energy/power in)) x 100

65
Q

How do you calculate kinetic energy?

A

1/2 x mass x velocity^2

66
Q

How do you calculate gravitational potential energy?

A

mass x gravity x height

A-Level Physics (15 decks)

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