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GCSE Physics > Forces > Flashcards

Forces Flashcards

(85 cards)

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1
Q

Which measurements are scalar?

A

(have magnitude only) speed, distance, time, momentum, mass

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2
Q

Which measurements are vectors?

A

(have magnitude and an associated direction) velocity, acceleration, displacement, force

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3
Q

State Newton’s First Law

A

If the resultant force acting on an object is zero and: • the object is stationary, the object remains stationary • the object is moving, the object continues to move at the same speed and in the same direction. So the object continues to move at the same velocity.

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4
Q

State Newton’s Second Law

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

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5
Q

State the equation explaining Newton’s Second Law

A

Force = mass x acceleration F = m x a

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6
Q

State Newton’s Third Law

A

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

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7
Q

Define inertia

A

The tendency of objects to continue in their state of rest or of uniform motion

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8
Q

State the equation explaining inertia

A

inertial mass = force ÷ acceleration

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9
Q

Define stopping distance

A

Thinking distance + braking distance

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10
Q

Define thinking distance

A

the distance the vehicle travels during the driver’s reaction time

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11
Q

State factors affecting thinking distance

A

distraction alcohol drugs caffeine speed tiredness

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12
Q

Define braking distance

A

the distance the car travels under the braking force

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13
Q

State factor affecting braking distance

A

Wet or icy road (road/weather conditions) brake (pads) condition tyre conditions speed weight (of the car and passengers)

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14
Q

State the equation explaining momentum

A

momentum = mass x velocity

p = m x v

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15
Q

Explain conservation of momentum

A

momentum before = momentum after Momentum will remain equal in a closed system

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16
Q

Define a closed system

A

a system where no external forces act

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17
Q

State the equation explaining change in momentum

A

force = change in momentum ÷ time

force = (final momentum - initial momentum) ÷ time

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18
Q

Explain how seat-belts use momentum for safety

A
  • seat-belts stretch - they decrease the speed (deceleration) of the crash - they increase the time taken to stop - they decrease the rate of change in momentum - less force is exerted on the person
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19
Q

State examples of how momentum is used for safety

A

Air bags seat-belts crumple zones bending your legs when landing

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20
Q

State the equation for constant/uniform acceleration

A

final velocity - initial velocity = 2 x acceleration x distance v² - u² = 2as

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21
Q

Define terminal velocity

A

Maximum velocity - reached when the resistive force (air resistance) is equal to the forward force (gravitational force/ acceleration), so the resultant force is zero

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22
Q

what factors affect the speed at which people walk, run or cycle?

A

age, terrain, fitness and distance travelled

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23
Q

walking speed

A

1.5 m/s

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24
Q

running speed

A

3 m/s

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25
cycling speed
6 m/s
26
speed of sound in the air
330 m/s
27
car speed
25 m/s
28
train speed
55 m/s
29
plane speed
250 m/s
30
equation for distance travelled
distance travelled = speed x time s = v t (m = m/s x s)
31
how to find speed on a distance - time graph
find the gradient
32
equation to find acceleration
acceleration = change in velocity / time
33
how to find acceleration on a velocity - time graph
gradient of the line
34
how to find distance travelled on a velocity - time graph
area under the graph
35
acceleration of a free falling object on earth
Near the Earth’s surface any object falling freely under gravity has an acceleration of about 9.8 m/s2
36
define inertial mass
inertial mass is a measure of how difficult it is to change the velocity of an object, • inertial mass is defined as the ratio of force over acceleration
37
state a typical reaction time
reaction time varies from 0.2-0.9 seconds
38
typical stopping distance at 30 mph
9m + 14m = 23m
39
typical stopping distance at 50 mph
15m + 38m = 53m
40
typical stopping distance at 70 mph
21m + 75m = 96m
41
how braking works
When a force is applied to the brakes of a vehicle, work done by the friction force between the brakes and the wheel reduces the kinetic energy of the vehicle and the temperature of the brakes increases
42
explain the dangers caused by large decelerations
Large decelerations may lead to brakes overheating and/or loss of control (The greater the speed of a vehicle the greater the braking force needed to stop the vehicle in a certain distance.)
43
when does change in momentum occur?
When a force acts on an object that is moving, or able to move, a change in momentum occurs
44
explain how are vectors represented?
A vector quantity may be represented by an arrow. The length of the arrow represents the magnitude, and the direction of the arrow the direction of the vector quantity.
45
define a force
A force is a push or pull that acts on an object due to the interaction with another object. • contact forces – the objects are physically touching • non-contact forces – the objects are physically separated.
46
examples on non-contact forces
gravitational force, electrostatic force and magnetic force
47
examples of contact forces
friction, air resistance, tension and normal contact force
48
define weight
Weight is the force acting on an object due to gravity. The force of gravity close to the Earth is due to the gravitational field around the Earth.
49
equation for weight
weight = mass × gravitational field strength W = m g (weight of an object and the mass of an object are directly proportional)
50
how is weight measured?
using a calibrated spring-balance (a newtonmeter)
51
define resultant force
A number of forces acting on an object may be replaced by a single force that has the same effect as all the original forces acting together (the resultant force)
52
when is work done
When a force causes an object to move through a distance, so a force does work on an object when the force causes a displacement of the object.
53
equation for work done
work done = force × distance W = F s (1 joule = 1 newton-metre)
54
how can forces change objects' shape?
compress, stretch and bend (only on stationary objects) there must be TWO FORCES for this to happen
55
what happens if only one force acts on an object?
the object will just move in the direction of that force (not change shape)
56
elastic deformation
an elastically deformed object will return to it original shape when the force stops (spring being stretched)
57
inelastic deformation
an inelastically deformed object will not return to its original shape when the force stops (car after a crash)
58
connection between extension and force
The extension of an elastic object, such as a spring, is directly proportional to the force applied, provided that the limit of proportionality is not exceeded.
59
equation for extension/compression and force
force = spring constant × extension F = k e
60
equation for elastic potential energy
elastic potential energy = 0.5 × spring constant ×extension2 (Ee = 0.5 k e2)
61
equation for moments
**moment of a force = force × distance** (moment of a force is in _newton-metres_, Nm force is in _newtons_, N distance is the _perpendicular distance from the pivot to the line of action of the force_, in _metres_, m.)
62
define moment of a force
The **turning effect of a force** is called the moment of the force (A force or a system of forces may cause an object to _rotate_.)
63
exampls of forces causing rotation
see-saw door handles wrench
64
define a moment
A force or a system of forces may cause an object to rotate
65
what is a fluid?
can be either a liquid or a gas
66
pressure at the surface of a fluid can be calculated using the equation:
pressure = force normal to a surface/ area of that surface (p = F A) pressure, p, in pascals, Pa force, F, in newtons, N area, A, in metres squared, m2
67
what does a pressure in fluids cause?
a force normal (at right angles) to any surface
68
The pressure due to a column of liquid can be calculated using the equation:
pressure = height of the column × density of the liquid × gravitational field strength [p = h ρ g] pressure, p, in pascals, Pa height of the column, h, in metres, m density, ρ, in kilograms per metre cubed, kg/m3
69
explan why density in a liquid affects pressure
more dense = more particles in a given area, therefore more particles are able to collide and create pressure
70
what is atmospheric pressure?
the force per unit area created by the weight of the air (particles) in the atmosphere Air molecules colliding with a surface create atmospheric pressure.
71
what is pressure?
the force per unit of area
72
explain upthrust
A partially (or totally) submerged object experiences a greater pressure on the bottom surface than on the top surface. This creates a resultant force upwards. This force is called the upthrust.
73
what is upthrust equal to?
upthrust = weight of water displaced
74
explain how ships float?
if the ships weight is equal to the upthrust then it floats, thus depends on density of the ship: if the ship is less dense than water it floats ---\> a smaller volume of the ship in water is equal to its weight
75
explain why depth in a liquid affects the pressure
76
explain how a submarine works
to sink: fills a tank with water to increase density to float: fills a tank with air to decrease density
77
what is the atmosphere?
The atmosphere is a thin layer (relative to the size of the Earth) of air round the Earth. The atmosphere gets less dense with increasing altitude
78
explain how atmospheric pressure increases with altitude
The number of air molecules (and so the weight of air) above a surface decreases as the height of the surface above ground level increases. So as height increases there is always less air above a surface than there is at a lower height. So atmospheric pressure decreases with an increase in height.
79
equation for change in pressure
_change in pressure_ = density (of liquid) x gravitational field strength x _change in depth_
80
describe why an object is balanced
If an object is balanced, the total clockwise moment about a pivot equals the total anticlockwise moment about that pivot.
81
what do lever/gear systems do?
A simple lever and a simple gear system can both be used to **transmit the rotational effects of forces**
82
what changes during circular motion?
distance therefore velocity therefore acceleration constantly change
83
what is circular motion?
An object moving at a constant speed in a circle
84
how levers works?
We can use levers to increase the distance between the pivot and where we’re applying the force. (the further from the pivot the less force needed to lift the same mass)
85
how do gears work?
gears have _interlocking teeth_ so as one gear turn another _turns in the opposite direction_ a larger gear _increases the moment_ as the _distance from the pivot_ (edge to centre) increases

GCSE Physics (5 decks)

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