P10 forces and motion Flashcards

1
Q

what is acceleration?

A

the change in velocity over a given time

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2
Q

what is decceleration?

A

when an object slows down (negative acceleration)

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3
Q

how do you calculate acceleration from a VELOCITY time graph?

A

the gradient of the graph

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4
Q

what is the initial acceleration of an object falling to the earth?

A

approximately 9.8m/s2

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5
Q

what is the acceleration of a falling object due to?

A

the force of gravity acting on the object

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6
Q

what do air particles cause on a falling object?

A

an upward force of friction to act on the object called air resistance

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7
Q

what is terminal velocity?

A

when the force of air resistance balances the force of gravity so the object stops accelerating and reaches a constant velocity

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8
Q

where does terminal velocity apply?

A

to any falling object through a fluid

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9
Q

what affects the terminal velocity of an object?

A

the shape of the object affects the amount of air resistance on the object. this affects the terminal velocity

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10
Q

what is Newton’s first law of motion?

A

if the resultant force of a stationary object is 0, it will remain stationary
if the resultant force of a moving object is 0, the object will continue to move with the same velocity

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11
Q

what is Newton’s second law of motion?

A

the acceleration of an object is proportional to the resultant force acting on the object and inversely proportional to the mass of the object
aka - F=ma

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12
Q

what are the typical speeds of a car on the motorway and a normal road?

A

approx. 13 m/s on a typical road
approx. 30 m/s on a motorway

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13
Q

what is the typical acceleration of a car travelling from a road to a motorway?

A

2 m/s2

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14
Q

what is another way of describing Newton’s first law?

A

objects will stay still or continue to move with constant motion unless you apply a resultant force

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15
Q

what is inertia?

A

the tendency for an object to stay at rest or continue in uniform motion (due to Newton’s 1st law)

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16
Q

what is inertial mass?

A

a measure of the difficulty of changing an object’s velocity

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17
Q

what is Newton’s third law of motion?

A

whenever two objects interact, they exert equal and opposite forces on each other

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18
Q

what do all moving objects have?

A

momentum

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19
Q

what is the value of a stationary object’s momentum?

A

0

20
Q

what is the conservation of momentum?

A

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

21
Q

what is momentum?

A

the product of an objects mass and velocity

22
Q

what is the unit for momentum?

A

kg m/s

23
Q

why are rapid changes in momentum dangerous?

A

they can cause large impact forces be exerted on an object/person, causing an injury

24
Q

what are crash tests used for?

A

to help car manufacturers design car safety features

25
Q

which two equations can be combined together to calculate the force of an object using its change in momentum?

A

F = ma
a = change in velocity / time
to make F = (m x v) / t (this is given in the exam)

26
Q

how can the danger of rapid changes in momentum be reduced?

A

the overall force acting on the person can be reduced by increasing the time taken for the change in momentum to take place. this is due to the equation F = mv / t where an increase in t reduces the overall force.

27
Q

what are some safety devices which slow down momentum change?

A

airbags
seatbelts
helmets
crash mat
cushioned surfaces

28
Q

what is stopping distance?

A

the distance from when the driver first sees the obstruction to when the car actually stops

29
Q

what are the two parts of stopping distance?

A

thinking distance
braking distance

30
Q

what is thinking distance?

A

the distance travelled by the car during the driver’s reaction time

31
Q

what is braking distance?

A

the distance the car travels from when the driver applies the brakes to when it stops

32
Q

what is reaction time?

A

the time it takes for the driver to spot the obstruction, make a decision and then put their foot to the brake

33
Q

how is the stopping distance affected due to the speed of the car?

A

the greater the speed, the greater the stopping distance (assuming the same force is being applied to the brakes)

34
Q

what affects reaction time and stopping distance?

A

tiredness, drugs, distractions

35
Q

what affects braking distance?

A

adverse road conditions (icy or wet), poorly maintained vehicles

36
Q

what happens to the kinetic energy of a car if its velocity doubles?

A

it quadruples (x4)

37
Q

what are the energy transfers involved with braking a vehicle?

A

the kinetic energy is transferred to thermal energy in the brakes due to the friction between the wheel and the brake
the temperature increases and the car slows down

38
Q

if the speed of a car is increased, what happens to the braking force required to stop the car in a given distance?

A

the braking force increases

39
Q

what can rapid deceleration cause in a car?

A

the brakes can overheat
the driver can lose control very quickly

40
Q

what is an elastic object?

A

an object which returns to its original shape when the forces deforming it are removed

41
Q

what are the conditions for elastic deformation?

A

an elastic material, at least two forces acting on the object

42
Q

what would happen if only one force is applied to an elastic object?

A

the stationary object would move instead of being elastically deformed as the forces are no longer balanced

43
Q

what is an inelastic material?

A

a material which does not return to its original shape when the forces deforming it are removed

44
Q

what is inelastic deformation?

A

when an inelastic object has forces exerted on it and does not return to its original shape

45
Q

what is Hooke’s law?

A

the extension of a spring is directly proportional to the force applied as long as the limit of proportionality is not exceeded

46
Q

what is the limit of proportionality of a spring?

A

the limit for Hooke’s law applied to the extension of a stretched spring

it is when the spring no longer returns to its original length

47
Q

what is the spring constant of a spring?

A

the force per unit extension needed to extend the spring.
it is a measure of the stiffness of the spring