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physics > 3.2 Forces in action > Flashcards

3.2 Forces in action Flashcards

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1
Q

if you apply a net force on an object, what will happen

A

the object will accelerate in the direction of the net force

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2
Q

what equation relates force mass and acceleration

A

F=ma

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3
Q

complete the sentence: a force of 1 Newton will give…

A

a 1kg mass an acceleration of 1ms-2 in the direction of the force

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4
Q

what is the difference between weight and mass

A

mass: constant for a specific object or particle (kg)
weight: magnitude is variable- depends on the location (N)

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5
Q

what instrument can be used to determine the weight of an object

A

newtonmeter

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6
Q

what is weight

A

gravitational force acting on an object through its centre of mass

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7
Q

what is friction

A

the force that arises once two surfaces rub against eachother

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8
Q

what is drag

A

the resistance force on an object through a fluid (gas or liquid) (same as friction)

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9
Q

what is tension

A

the force within a stretched cable or rope

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10
Q

what is upthrust

A

an upward force acting on an object when it is in a fluid

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11
Q

what is normal contact force

A

a force arising when one object rests against another object

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12
Q

how are forces represented in a free-body diagram

A

-each vector is represented by an arrow labelled with the force it represents
-each arrow is drawn to the same scale (larger force= longer arrow)

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13
Q

what is meant by the term fluid

A

a substance that has no particular shape and yields easily to external pressure (gas or liquid)

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14
Q

what is the magnitude of drag dependent on

A

speed and cross sectional area

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15
Q

how is drag related to speed

A

drag is directly proportional to speed^2 (speed doubled - drag increases by 4)

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16
Q

describe how the forces of weight and drag change when an object undergoes a vertical fall

A

the weight of the object stays constant however drag increases as speed increases

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17
Q

what is the magnitude of the drag force at the instant to object when it first begins to fall

A

theres no drag on the object- force is equal to the weight

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18
Q

what is terminal velocity

A

when drag is equal and opposite to its weight

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19
Q

what is centre of gravity

A

this is the point where we can consider the weight of the object to be acting

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20
Q

what is centre of mass

A

if one fore acts in a body and its line of action passes through this point it will cause no rotation

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21
Q

what is location of the centre of mass of a uniform metre ruler

A

50cm (0.5m)

22
Q

what is meant by equilibrium

A

when the resultant force is equal to zero

23
Q

explain why when an object is in equilibrium the forces acting on it must form a closed triangle

A

the triangle is closed because the net force is zero and so the object is in equilibrium

24
Q

if an object is in equilibrium what does this mean in terms of the horizontal and vertical forces acting on the object

A

the resultant force vertically must be zero and resultant horizontal force must also be zero

25
Q

how do you calculate the horizontal and vertical components of a force

A

Tcosθ=F Tsinθ=F (respectively)

26
Q

what is meant by the moment of a force

A

the turning effect of a force about an axis or point

27
Q

how is the moment of the force defined

A

force x perpendicular distance of the line from the point of action

28
Q

what is the SI unit for the moment of a force

A

Nm

29
Q

state the principle of moments

A

the sum of clockwise moments is equal to the sum of anticlockwise moments

30
Q

how can you make an object rotate without there being any transitional motion

A

apply equal but opposite forces to the object

31
Q

what is a couple

A

a pair of equal parallel forces acting in opposite directions and along different lines

32
Q

what is torque

A

the measure of the force that can cause an object to rotate about an axis

33
Q

how is torque defined

A

torque of a couple = one of the forces x perpendicular separation between the forces = Fd

34
Q

what are the units of torque

A

Nm

35
Q

how is density defined

A

mass per unit volume

36
Q

how is density defined

A

ρ=m/V

37
Q

what are the SI units of density

A

kgm-3

38
Q

describe how you would determine the density of a regular shaped solid

A

mass can be measured directly using a digital balance and volume can be calculated by measurements taken with a ruler or micrometer

39
Q

describe how you would determine the density of an irregular shaped solid

A

mass can be measured directly using a digital balance and volume can be determined by displacement of water when placed into a measuring cylinder

40
Q

describe how you would determine the density of a liquid

A

mass can be measured directly using a digital balance and volume can be measured directly using a measuring cylinder

41
Q

how is pressure defined in words

A

normal force exerted per unit cross-sectional area

42
Q

how is pressure calculated

A

p=F/A pressure=force/ area

43
Q

what is the SI units of pressure

A

Nm-2 or Pa

44
Q

what is a fluid

A

substance that can flow (gases and liquids)

45
Q

explain why gases and liquids exert pressure on surfaces

A

because of the constant bombardment by their molecules- liquids are the same

46
Q

state the equation that can be used to calculated pressure exerted by a vertical column of a liquid

A

p=hρg

47
Q

what does the equation p=hρg show

A

pressure is not dependent on the cross sectional area, pαh so water pressure is increased with depth, denser liquids will exert greater pressure, the pressure is the same in all directions

48
Q

what is upthrust

A

a buoyant force- upward force

49
Q

why do objects submerged in water experience an upward force

A

the pressure difference at upper and lower surfaces

50
Q

state Archimedes principle

A

the upthrust is equal to the weight of the fluid displaced

51
Q

what condition is required for an object to sink

A

if the objects weight is greater than the upthrust

52
Q

what condition is required for an object to float

A

upthrust must be equal to the weight of the object

physics (20 decks)

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