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Forces 2 Flashcards

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1
Q

vector quantity

A

a quantity that has both magnitude and direction

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2
Q

Examples of vector quantities

A

force, velocity, displacement, acceleration, momentum

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3
Q

scalar quantity

A

a quantity that can be described by magnitude only and has no direction

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4
Q

Examples of scalar quantities

A

speed, distance, time, mass, temperature

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5
Q

How are vectors represented?

A

With arrows - the length shows the magnitude and the direction of the arrow shows the direction of the vector.

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6
Q

Force

A

A push or a pull on an object that is caused by it interacting with something

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7
Q

Two types of forces

A

contact and non-contact

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8
Q

contact force

A

When two objects have to be touching for a force to act

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9
Q

Examples of contact forces

A

friction, air resistance, tension and normal contact force

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10
Q

non-contact force

A

Objects DO NOT need to be touching for the force to act

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11
Q

Examples of non-contact forces

A

Magnetic, gravitational, electrostatic

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12
Q

interaction pair

A

A pair of forces that are equal and opposite and act on two interacting objects

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13
Q

What does gravity do?

A

Attracts all masses

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14
Q

What effects does gravity have?

A

1) on the surface of a planet it makes all things fall towards the ground.

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15
Q

Mass

A

the amount of matter in an object

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16
Q

Weight

A

The force acting on an object due to gravity

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17
Q

What varies gravitational field strength?

A

Location

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18
Q

What does the weight of an object depend on?

A

the strength of the gravitational field at the location of the object

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19
Q

Units for weight

A

Newtons

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20
Q

Centre of mass

A

A point at which you assume the whole mass is concentrated

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21
Q

What is weight measured using?

A

A calibrated spring-balance (newtonmeter)

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22
Q

Weight equation

A

Weight (n)=Mass(kg) x gravitation field strength (m/s^2)

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23
Q

Increasing the mass of an object

A

Increases its weight

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24
Q

Weight and mass are

A

directly proportional

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25
Q

What do free body diagrams show?

A

all forces acting on an isolated object

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26
Q

What do the sizes of the arrows on a free body diagram show?

A

The relative magnitudes of the forces

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27
Q

Resultant force

A

The overall force on a point or object

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28
Q

How to calculate resultant force?

A

Adding the forces going in the same direction and subtracting forces going in opposite directions

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29
Q

What happens when a force moves an object through a distance?

A

Energy is transferred and work is done on the object

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30
Q

Work done equation

A

Work done(J)= Force(N) x distance(M)

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31
Q

1 joule equals

A

1 newton meter

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32
Q

How do we use scale drawings to find resultant forces?

A

1) draw all the forced acting on an object, to scale, tip-to -tail

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33
Q

Equilibrium

A

When all the forces acting on a object combine to give a resultant force of zero

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34
Q

How to split a force into components

A

Split them at right angles on grid lines and draw horizontal and vertical components along the lines to measure them

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35
Q

What happens when you apply a force on a object?

A

You may cause it to stretch, compress, or bend

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36
Q

Elastically deformed

A

If an object can go back to its original shape and length after the force has been removed.

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37
Q

What are elastically deformed objects known as?

A

Elastic objects

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38
Q

Inelastically deformed

A

Object doesn’t return to its original shape and length after force has been removed

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39
Q

What happens when a force stretches or compresses an objects?

A

Work is done and causes energy to be transferred to the elastic potential energy store of the object

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40
Q

The extension of a stretched spring is…

A

directly proportional to the load or force applied

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41
Q

Force-extension equation

A

Force = spring constant x extension

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42
Q

What does the spring constant depend on?

A

The material that you are stretching- a stiffer spring has a greater spring constant

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43
Q

Force against extension graph

A

The curve in the graph shows the maximum force where extension is no longer proportional. This is known as limit of proportionality and is shown on the graph at the point marked P. The axes can also be flipped.

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44
Q

Limit of proportionality

A

The limit beyond which, when a wire or spring is stretched, its extension is no longer proportional to the force that stretches it.

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45
Q

Investigating the link between force and extension practical

A

Equipment:

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46
Q

Pilot experiment to check the masses are a good size

A

Using an identical spring to the one you’ll be testing , load it with masses one at a time up to a total of five. Measure the extension each time you add another mass.

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47
Q

elastic potential energy equation

A

0.5 x spring constant x extension^2

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48
Q

moment

A

The turning effect of a force

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49
Q

Moment equation

A

moment = force x perpendicular distance from pivot

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50
Q

What causes a larger moment?

A

A larger force or a longer distance

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51
Q

Maximum moment

A

To get the maximum moment, you need to push at right angles to the spanner.

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52
Q

What does it mean if the total anti-clockwise moment equals the total clockwise moment?

A

The object is balanced and won’t turn

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53
Q

What do levers do?

A

They increase the distance from the pivot at which the force is applied. This means less force is needed to get the same moment

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54
Q

gears

A

A set of wheels with teeth that interlock so that turning one causes another to turn in the opposite direction. They are used to transmit the rotational effect of a force from one place to another.

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55
Q

What do different sizes gears do?

A

They change the moment of the force

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56
Q

Fluids

A

Substance that can flow because their particles are able to move around

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57
Q

What is pressure?

A

Force per unit area.

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58
Q

Pressure of a fluid

A

a force is exerted at right angles to any surface in contact with the fluid

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59
Q

pressure at the surface of a fluid equation

A

Force normal to a surface / area of that surface

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60
Q

Density

A

Measure of the compactness of a substance

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61
Q

The more dense a liquid is…

A

the more particles it has in a certain space

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62
Q

What does more particles mean?

A

Higher pressure

63
Q

What happens as depth of a liquid increases?

A

The number of particles above that point increases. The weight of these particles adds to the pressure felt at that point, so liquid pressure increases with depth

64
Q

Pressure in a fluid equation

A

p = hρg

65
Q

upthrust on objects in fluids

A

When an object is submerged in a fluid, the pressure of the fluid exerts a force on it from every direction. Pressure increases with depth so the force exerted on the bottom of the object is larger than the force acting on top of the object. This causes a resultant force upwards known as upthrust.

66
Q

What is upthrust equal to?

A

The weight of fluid that has been displaced by the object

67
Q

What causes an object to float?

A

When upthrust is equal to weight

68
Q

What causes an object to sink?

A

When weight is greater than upthrust

69
Q

What happens when an object is less dense than the fluid it is placed in?

A

The object weighs less than the equivalent volume of fluid

70
Q

What happens when an object is denser than the fluid it is placed in?

A

it is unable to displace enough fluid to equal its weight

71
Q

atmospheric pressure

A

Pressure created on a surface by air molecules colliding with the surface

72
Q

What causes atmospheric pressure to decrease?

A

Increase in altitude, as the atmosphere gets less dense, so there are fewer air molecules that are able to collide with the surface

73
Q

distance

A

How far an object moves. It is a scalar quantity

74
Q

Dispalcement

A

Distance and direction of an object’s change in position from the starting point.

75
Q

scalar quantity

A

a quantity that can be described by magnitude only and has no direction

76
Q

vector quantity

A

a quantity that has both magnitude and direction

77
Q

speed/velocity

A

Both measure how fast you’re going but speed is scalar and velocity is vector

78
Q

Speed

A

how fast an object is moving with no regard to the direction

79
Q

Velocity

A

Speed in a given direction

80
Q

Distance and speed equation

A

S=vt

81
Q

typical speeds

A

walking - 1.5 m/s

82
Q

Acceleration

A

Change in velocity in a certain amount of time

83
Q

Acceleration equation

A

acceleration = change in velocity / time

84
Q

Constant acceleration is known as

A

Uniformed acceleration

85
Q

acceleration of gravity on Earth

A

9.8 m/s^2

86
Q

uniform acceleration equation

A

v² - u² = 2as

87
Q

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

A

speed

88
Q

Flat sections on a distance time graph

A

stationary

89
Q

Straight uphill sections on a distance time graph

A

travelling at a steady speed

90
Q

Curves on a distance time graph

A

Acceleration or deceleration

91
Q

Steepening curve on a distance-time graph

A

speeding up

92
Q

A levelling off curve on a distance-time graph

A

slowing down

93
Q

How to find the speed of an object that’s accelerating on a distance time graph?

A

Mark a point

94
Q

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

A

acceleration

95
Q

Flat sections on a velocity time graph

A

steady speed

96
Q

Steeper the graph on a velocity time graph

A

the greater the acceleration or deceleration

97
Q

Uphill sections on a velocity time graph

A

acceleration

98
Q

Downhill sections on a velocity time graph

A

deceleration

99
Q

Curve on a velocity time graph

A

changing acceleration

100
Q

Area under velocity-time graph

A

distance travelled

101
Q

How to find area under an irregular velocity time graph?

A

By counting the squares under the line and multiplying the number by the value of one square

102
Q

If an object has no force propelling it…

A

It will always slow down and stop because of friction

103
Q

Friction always acts

A

In the opposite direction of movement

104
Q

How is friction caused?

A

Two surfaces in contact

105
Q

Drag

A

Resistance in a fluid

106
Q

As speed increases

A

drag increases

107
Q

Terminal velocity in falling objects

A

When an object falls, the force of gravity is much more than the frictional force slowing it down so it accelerates. As the speed increases the friction builds up. This gradually reduces the acceleration until eventually the frictional force is equal to the accelerating force( so the resultant force is zero). It will have reached its maximum speed or terminal velocity and will fall at a steady speed.

108
Q

What does terminal velocity depend on?

A

shape and area and drag

109
Q

Newton’s First Law

A

If the resultant force on a stationary object is zero, the object will remain stationary. If the resultant force on a moving object is zero, it’ll just carry on moving at the same velocity (same speed and direction)

110
Q

A non zero resultant force will always produce

A

Acceleration or deceleration in the direction of the force

111
Q

What 5 forms can acceleration take?

A

starting, stopping, speeding up, slowing down, changing direction

112
Q

The larger the resultant force acting on an object…

A

the more the object accelerates

113
Q

Force and acceleration are

A

directly proportional

114
Q

Acceleration is inversely proportional to

A

the mass of the object

115
Q

Newton’s Second Law

A

F=ma

116
Q

Inertia

A

The tendency of an object to continue in the same state of motion

117
Q

inertial mass

A

A measure of how difficult it is to change the velocity of an object

118
Q

How to find inertial mass

A

Rearranging Newton’s second law into m=f/a

119
Q

Newton’s Third Law

A

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

120
Q

In Newton’s third law two forces are acting on

A

Different objects

121
Q

Investigating Motion - Method

A

1) Set up the apparatus. Set up the trolley so it holds a piece of card with a gap in the middle that will interrupt the signal on the light gate twice. If you measure the length of each bit of card that will pass through the light gate & input this into the software, the light gate can measure the velocity for each bit of card - can use this to work out the trolley’s acceleration

122
Q

Investigate the effect of masses

A

Add masses to the trolley one at a time to increase the mass of the system. Don’t add masses to the hook or you’ll change the force. Record the average acceleration for each mass

123
Q

Investigate the effect of force

A

Keep the total masses of the system the same, but change the mass on the hook. Start with all the masses loaded onto the trolley and transfer the masses to the hook one at a time to increase the accelerating force. The mass of the system stays the same as you’re only transferring the masses from one part of the system to the hook. Record average acceleration for each force

124
Q

How can Newton’s second law be used to explain the results of the investigating motion practical?

A

F=weight of the hanging masses

125
Q

stopping distance formula

A

Stopping distance = thinking distance + braking distance

126
Q

Thinking distance

A

How far the car travels during the driver’s reaction time

127
Q

Braking distance

A

The distance taken to stop under the braking force

128
Q

Typical car braking distances

A

14m at 30mph

129
Q

Thinking distance is affected by

A

Your speed and your reaction time

130
Q

Braking distance is affected by

A

Your speed

131
Q

braking relies on

A

Friction between the brakes and wheels

132
Q

What happens when a brake pedal is pushed?

A

The brake pads are pressed onto the wheels, thus causing friction, which causes work to be done. The work done between the brakes and the wheels transfers energy from the kinetic energy stores of the wheels to the thermal energy stores of the brakes, which as a result, increase in temperature

133
Q

What does a faster vehicle need?

A

A greater braking force

134
Q

A larger braking force means…

A

larger deceleration

135
Q

Typical reaction time

A

in between 0.2 - 0.9

136
Q

What affects reaction time?

A

Tiredness, drugs, alcohol, distractions

137
Q

Experiments to investigate reaction time

A

Computer based test and ruler drop test

138
Q

Ruler drop test method

A

Sit with your arm resting on the edge of a table. Get someone to hold a ruler so it hangs between your thumb and forefinger, lined up with zero

139
Q

What does speed affect?

A

Stopping distance

140
Q

As a car speeds up what happens to thinking distance?

A

it increases at the same rate as speed - graph is linear because thinking time stays pretty constant

141
Q

As a car speeds up what happens to braking distance?

A

it increases faster the more you speed up as the work done to stop the car is equal to the kinetic energy of the car which is 1/2 x mass x SPEED SQUARED

142
Q

Momentum

A

The product of an object’s mass and velocity

143
Q

The greater the mass or velocity of an object…

A

the more momentum the object has

144
Q

Momentum is a

A

vector quantity as it has size and direction

145
Q

momentum equation

A

P=mv (momentum(Kg/s) = mass(kg) x velocity(m/s))

146
Q

conservation of momentum

A

In a closed system the total momentum before an event is the same after the event

147
Q

If the momentum before an event is zero…

A

The momentum after will also be zero

148
Q

What can conservation of momentum be used to calculate?

A

Velocity or mass

149
Q

Change in momentum

A

When a non zero resultant force acts on a moving object it causes velocity to change. This means there is a change in momentum

150
Q

Change in momentum equation

A

Force (N) = change in momentum (kg m/s) / change in time (s)

151
Q

The force causing the change is equal to

A

rate of change of momentum

152
Q

A larger force means…

A

a faster change in momentum

153
Q

The longer it takes for a change in momentum…

A

the smaller the rate of change of momentum and so the smaller the force

Physics (6 decks)

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