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Physics > topic 5 - forces > Flashcards

topic 5 - forces Flashcards

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1
Q

What is moment?

A

the turning effect of a force

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2
Q

What is equation to calculate moment?

A

moment (Nm) = force (N) x distance (m)

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3
Q

How is the distance measured in moments?

A

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

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4
Q

if an object is in equilibrium, what can be said about the moments acting on the object?

A

the sum of the clockwise moment about the pivot is equal to the sum of the anticlockwise moment about the pivot

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5
Q

What is the function of a lever?

A

A lever allows us to lift a heavy object by applying a relatively small amount of force

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6
Q

Explain how a lever can act as a force multiplier

A
  • Force is applied further from the pivot.
  • Using a lever means less force is needed to get the same moment
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7
Q

Describe what a gear is and what function it serves in machinery.

A

A gear is a circular disc with teeth
- in machinery, it is interlocked with other gears in order to transmit the rotational effects of a force from one place to another

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8
Q

what is a fluid?

A

either a liquid or a gas

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9
Q

in any fluid, at what angle do the forces due to pressure act on a given surface?

A

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

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10
Q

what is the equation for pressure?

A

pressure = force/area

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11
Q

what happens to the density of the atmosphere with increasing altitude?

A

At increasing altitudes, density decreases

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12
Q

why does atmospheric pressure decrease with an increase in height?

A
  • the pressure is created by collisions of air molecules
  • the quantity of molecules decreases as the height increases
  • this means atmospheric pressure decreases with an increase of height
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13
Q

what is the Earth’s atmosphere?

A

a thin layer of air around the earth

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14
Q

How does the pressure in fluids increase with depth?

A
  • as the depth increases, the mass of liquid above that depth also increases
  • this means that the force is due to the mass increase
  • since the force has increased whilst the area has remained constant
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15
Q

why does the pressure in fluids increase with density?

A
  • As the density of a fluid increases, the number of particles in a given volume increases
  • consequently, the weight of the fluid is greater
  • this means that the force from the fluid above a certain point is larger. Since the force has increased, the pressure also increases
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16
Q

what equation shows the magnitude of pressure in liquids at different depths?

A

pressure = height x density x gravitational field strength

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17
Q

what is upthrust always equal to?

A

the weight of the fluid that the object displaces

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18
Q

what factors influence whether an object will sink or float?

A
  • upthrust
  • weight
  • density of fluid
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19
Q

what is the equation used to calculate an object’s moment?

A

moment = mass x velocity

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20
Q

what is the unit used for momentum?

A

kgm/s

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21
Q

what is meant by “momentum is conserved”?

A

total momentum before = total momentum after

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22
Q

what is the equation for change in momentum?

A

change in momentum = force x time

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23
Q

how does a seatbelt improve a passenger’s safety during a collision?

A
  • passenger must decelerate from the vehicle’s velocity at impact to zero, meaning they undergo a fixed change of momentum
  • the force they experience is equal to the rate of change of momentum
  • seatbelts increase the time over which the force is applied, reducing the rate of change of momentum and therefore reducing the force experienced
24
Q

why is momentum not always conserved in a collision?

A

external forces may act on the object too

25
Q

how do protective pads help to reduce injury when two people collide?

A
  • protective pads increase the time taken to come to a stop during the collision
  • the rate of change of momentum decreases, reducing the force applied onto the people
26
Q

other than collisions, what is another type of event where the conservation of momentum applies?

A

an explosion

27
Q

what are scalar quantities?

A

scalar quantities have magnitude only

28
Q

what are vector quantities?

A

vector quantities have magnitude and an associated direction

29
Q

what is force?

A

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

30
Q

what are examples of scalar quantities?

A
  • mass
  • temperature
  • speed
  • energy
  • distance
  • time
31
Q

what are examples of vector quantities?

A
  • displacement
  • weight
  • force
  • velocity
  • acceleration
  • momentum
32
Q

what is the unit of force?

A

Newtons (N)

33
Q

what are the two categories forces can be divided into?

A
  • contact forces
  • non-contact forces
34
Q

what are contact forces?

A

forces that need to be physically touching to interact

35
Q

what are non-contact forces?

A

forces that do not need to be physically touching to interact

36
Q

what are examples of contact forces?

A
  • friction
  • air resistance
  • tension
  • normal contact force
37
Q

what are examples of non contact forces?

A
  • gravitational force
  • electrostatic force
  • magnetic force
38
Q

what is weight?

A

weight is the force acting on an object due to gravity

39
Q

why is the force of gravity close to the Earth?

A
  • the force of gravity close to the Earth is due to the gravitational field
40
Q

what does the weight of an object depend on?

A
  • the weight of an object depends on the gravitational field strength at the point where the object is
41
Q

what is the equation to calculate the weight of an object?

A

weight (N) = mass x gravitational field strength

42
Q

what is meant by an object’s centre of mass?

A

the single point where an object’s weight can be considered to act through

43
Q

what piece of equipment can be used to measure an object’s weight?

A

a calibrated spring-balance (a newtonmeter)

44
Q

what is the relationship between the weight and mass of an object?

A
  • the weight of an object and the mass of an object are directly proportional
45
Q

what is the resultant force?

A
  • resultant force is the single force that is equivalent to all the other forces acting on a given object
46
Q

what does it mean if a force is said to do “work”?

A
  • the force causes an object to be displaced through a distance
47
Q

what is the equation used to calculate work done?

A

work done = force x distance

48
Q

what are the units for work done?

A

Joules

49
Q

what distance must be used when calculating work done?

A

it must be the distance that is moved along the line of action of the force

50
Q

what occurs when work is done against frictional forces?

A
  • a rise in temperature of the object occurs
  • kinetic energy is converted to heat
51
Q

what are the relationship between the force applied and the extention of an elastic object?

A
  • the extension is directly proportional to the force applied, provided that the limit of proportionality is not exceeded
52
Q

what is meant by an inelastic deformation?

A
  • a deformation which results in the object being permanently stretched
  • the object doesn’t return to its original shape when the force is removed
53
Q

what is the equation relating force?

A

force = spring constant x extension

54
Q

what are the units for spring constant?

A

(N/M)

55
Q

what type of energy is stored in a spring when it is stretched?

A

elastic potential energy

56
Q

what can extension be replaced with in the equation for spring force?

A

compression

57
Q

explain why different people will go at different speeds on the same zip wire

A
  • different people have different surface area
  • and hence different air resistance

Physics (8 decks)

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