P5:Forces Flashcards Preview

GCSE PHYSICS AQA (PAPER 2) > P5:Forces > Flashcards

Flashcards in P5:Forces Deck (138):
1

What do vector quantities have

•Magnitude •Direction

2

Physical quantities of vectors include ...

•force•velocity•displacement•acceleration•momentum

3

What is a scalar quantity

A physical quantity that only contains magnitude and NOT DIRECTION

4

Scalar quantities include...

•Speed•Distance •Mass•Temperature •Time

5

What usually represents a vector, and what does this symbol show

Usually represented by an arrow •length of arrow represents magnitude •direction of arrow represents the direction of the quantity

6

Forces can be...

•contact (when to objects have to be touching for a force to act) E.G:friction, air resistance OR•non-contact (when an object doesn’t need to be touching for a force to act) E.G:magnetic force, gravitational force

7

A force is a...

Push or pull on an object that is caused by it interacting with something

8

When two objects interact...

There is a force produced on both sides

9

Define the term ‘interaction pair’

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

10

Gravitational force is...

The force of attraction between masses

11

What are gravity’s two main important effects

•on the surface of the planet, it makes all things fall towards the ground AND•it gives everything a weight

12

Define the term ‘mass’

The amount of of ‘stuff’ in an object

13

What is weight

Weight is the force acting on an object due to gravity.Close to the earth, this force is caused by the gravitational field around the eating

14

Gravitational field strength varies, where is it strongest

It’s stronger the closer you are to the mass and it’s stronger for larger masses

15

What does the weight of an object depend on?

The strength of a gravitational force at the location of the object. This means the weight of an object changes with location

16

Weight is measured in ...

Newtons

17

What is the term to describe the weight force acting from a single point on an object

‘Centre of mass’

18

Weight is measured using...

A calibrated spring balance or newtonmeter

19

Mass and weight are directly proportional. What equation would you use to work out the weight of an object?

Weight(N)=Mass(KG) x Gravitational Field Strength(N/KG)

20

Increasing the mass of an object increases his weight. Write this using the direct proportional symbol

W ∝ M

21

What can you use to show the forces acting on an object

A free body diagram

22

What do the things on a free body diagram represent

•The size of the arrows show the relative magnitudes of the forces •The direction show the direction of forces acting on the object

23

A resultant force is...

The overall force on a point or object

24

How many forces act on an object along any direction

At least two

25

If you have a number of forces acting at a singles point what can you replace them with

A single force AKA: the resultant force

26

If the forces all act along a parallel line, how is the overall effect found ...

By adding those going in the same direction and subtracting any force going in the opposite direction

27

If w resultant force moves an object through a distance...

Energy is transferred & work is done

28

To make something move...

A force must be applied

29

The thing applying the force needs...

A source of energy E.G:food or fuel

30

Work is done even if the energy transferred is ...

Useful or wasted

31

Equation for work done

Work Done(J)=Force(N) x Distance(m) W=FxS

32

One joule of work is done when a force of...

One newton caused an object to move a distance of one metre.

33

Conversion of joules to newton meters

1J = 1Nm

34

How to use a scale drawing to find a resultant force

1.Draw all the forces acting on an object, to scale ‘tip-to-tail’2.Draw a straight line from the start of the first force to the end of the last force (resultant force)3.Measure length of resultant force on the diagram to find the magnitude, angle and direction of the force

35

If all the forces acting on an object combine to give a resultant force of zero Or If the forces are balanced

The object is at an equilibrium

36

For three forces the scale diagram should...

Form a triangle

37

To draw an equilibrium the tip of the last force...

Should end where the tail of the first force you drew began

38

If told to find the missing force when an object is at equilibrium, you should

•draw out the forces you do know•join the end of the last force to the start of the first force•^ this line is the missing force so you can measure its size and direction

39

Not all forces act...

Horizontally or vertically, some are at awkward angles

40

If you find a force with an awkward angle...

•split it into two components at right angles (acting together these components have the same effect as the single force)

41

To resolve an single force...

•split it into components by drawing it on a grid •draw the force to scale•add horizontal and vertical components along grid lines •Then measure the components

42

When you apply a force to an object you may cause it to...

Stretch, compress or bend ^these actions transfer energy

43

If an object is being stretched, compressed or bent you need...

More than one force acting on the object otherwise the object would simply move in the direction of the applied force

44

An object has been elastically deformed if...

It can go back to its original shape and length after the force has been removed. They are called elastic objects E.G: a spring

45

An object has been inelastically deformed if...

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

46

Work is done when a forced stretches or compressed an object because...

Energy is transferred to the elastic potential energy store of the object

47

If work is done in an elastically deformed object...

ALL energy is transferred to the objects elastic potential energy store

48

Extension is directly proportionately to force

F ∝ e This is the equation:F(N)=K(N/m) x e(m)

49

The spring constant depends on...

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

50

The F=Ke equation also works for compression...

Where e is just the difference between the natural and compressed lengths (The compression)

51

There is a limit to the amount of force you can apply to an object...

To keep on increasing it proportionally

52

Distance is just how far an object has moved its has...

A scalar quantity

53

Displacement measures the distance and direction in w straight line from an objects starting point to its finishing point

It is a vector quantity E.G: a bearing

54

EXAMPLE:If you walk 5m north and 5m south...

Your displacement is 0 But the distance travelled is 10m

55

Speed and velocity both measure how fast you’re going, but...

•Speed is a scalar quantity •velocity is a vector quantity

56

you can have objects travelling at a constant speed with a changing velocity

When an object is changing direction whilst staying at the same speed E.G:a car going round a roundabout

57

If you want to measure the speed of an object moving with a constant speed you should...

Time how long it takes the object to travel a certain distance

58

The equation for measure an objects speed

Speed(m/s)= distance travelled(m) / time(s)V= m/s

59

Objects rarely travel at a constant speed, your speed is always changing...

The formula:V=s / tGives the average (mean) speed during that time period

60

A persons walking speed...

1.5m/s•many things can effect this, for example a persons fitness,age, distance travelled or the terrain

61

A persons running speed

3m/s•many things can effect this, for example a persons fitness,age, distance travelled or the terrain

62

A persons cycling speed

6m/s

63

A cars speed

25m/s

64

A trains speed

30m/s

65

A planes speed

250m/s

66

The speed of sound (330m/s in the air) changes depending on...

What the sound waves are travelling through, the speed of the wind

67

Wind speed can be affected by things like

•Temperature •atmospheric pressure •buildings in that area Or•structures near by

68

Acceleration is...

How quickly you’re speeding up, it is the change in velocity in a certain amount of time

69

Equation for acceleration

Acceleration (m/s {squared}) =

70

Uniform acceleration means...

A constant acceleration

71

Acceleration due to gravity is uniform for objects in free fall.

It’s roughly equally to 9.8m/s² bear the earths surface and has the same value as gravitational field strength

72

Equation for uniform acceleration

V² - U²= 2asFinal velocity(m/s) - initial velocity(m/s) = acceleration(m/s²) x distance (m)

73

To estimate an acceleration...

Use the typical speed of the object and ÷ by the time

74

Use distance time graphs to show...

An object moving on a straight line

75

Gradient = speed

The steeper the graph, the faster the speed

76

DTG:Flat sections

Stationary

77

DTG:Straight uphill

Travelling at a steady speed

78

DTG:Curve

Acceleration or deceleration

79

DTG:Steepening curve

Speeding up

80

DTG:Levelling off curve

Slowing down

81

Velocity time graphs show...

How an objects velocity changes

82

VTG:Gradient

Acceleration

83

VTG:Flat section

Steady speed

84

VTG:Steeper gradient

Greater acceleration or deceleration

85

VTG:Uphill sections (/)

Acceleration

86

VTG:Downhill sections(\)

Deceleration

87

VTG:A curve

Change in acceleration

88

The area under any section of the graph is...

Equal to the distance travelled in that time interval

89

If the graph is curved...

Use a tangent to the curve at a point to find the acceleration

90

If an object has no force propelling it along he will always...

Slow down and stop because of friction

91

Friction always acts in...

The opposite direction to movement

92

To travel at a stress speed...

The driving forces need to balance the frictional forces

93

You get friction between two surfaces in contact...

Or when an object passes through fluid (this is also know as drag)

94

You can reduce friction between surface by using...

Lubricant

95

Drag is the resistance you get in a...

Fluid (a gas or a liquid)•Air resistance is a type of drag

96

The most important factor by far in reducing drag is...

Keeping the shape of the object streamlined (This is where the object is designed to allow fluid to flow easily across it, reducing drag)

97

Parachutes work in the opposite way...

They want as much drag as they can get

98

Frictional Forces from fluids always...

Increase with speed(E.G: a car has much more friction to work against when travelling at 70mph compared to 30mph)

99

When a falling object first sets off, the force of gravity is much more...

Than the frictional force slowing it down, so it accelerates

100

When an object is falling, as the speed increases...

•The friction builds up, this gradually reduces the acceleration •Eventually the frictional force is equal to the accelerating force •The resultant force is zero •It will have reached its maximum speed or terminal velocity and will fall at a steady speed

101

Typically, the less streamlined an object is...

The lower it’s terminal velocity

102

Objects with a large surface area...

Tend to have lower terminal velocity as there is more air resistance acting on it at any given speed

103

Terminal velocity depends on shape and area

For example, if you dropped a marble and a beach ball off a tall building, the marbles terminal velocity would be higher than the terminal velocity of the beach ball.The beach ball spends less time accelerating before the air resistance is large enough to equal the accelerating force

104

Newton’s first law

A resultant force is needed to make something start moving, speed up or slow down •if the resultant force on a stationary object is zero, the object will stay stationary•if the resultant force on a moving object is zero, it will just carry on moving at the same velocity

105

A non zero resultant force will always...

Produce an acceleration or deceleration in the direction of the force •On a free body diagram, the arrows will always be unequal

106

Five different forms acceleration can take

•Starting•Stopping•Speeding up•Slowing down •Changing direction

107

Acceleration is proportional to the resultant force

F ∝ a

108

Acceleration is also...

Inversely proportional to the mass of the object

109

Newton’s second law

F= m aResultant force (N) = Mass(Kg) x Acceleration(m/s²)

110

To estimate the acceleration

Use the typical speed of an object and multiply it by the mass

111

Inertia is...

The tendency for motion to remain unchanged

112

An objects inertial mass measures how...

Difficult it is to change the velocity of an object

113

Inertial mass can be found using Newton’s second law

m= F ÷ a•inertial mass is just the ratio of a force over acceleration

114

Newton’s third law

When two objects interact, the forces the exert on each other are Raquel and opposite E.G:If you push a trolley, the trolley will push back against you just as hard & when you stop pushing, so does the trolley

115

An example of Newton’s third law is...

An equilibrium situation, but if the two forces are different types and not acting on the force this isn’t an example of Newton’s third law

116

In an emergency, a driver may perform an emergency stop...

This is where maximum force is applied by the brakes in order to stop the car in the shortest possible distance

117

The longer it takes to perform an emergency stop...

The higher the risk of crashing into what ever is infront if you

118

Distance it takes for a car to stop in an emergency is found by...

Stopping distance = thinking distance + braking distance

119

Thinking distance

How far the car travels during the drivers reaction time

120

Braking distance

The distance taken to stop under the braking force (once brakes are applied)

121

Breaking distance if a car is travelling at 30mph

14m

122

Breaking distance if a car is travelling at 60mph

55m

123

Breaking distance if a car is travelling at 70mph

70m

124

Thinking distance is affected by

•your speed - the faster you’re going the further you’ll travel during the time it takes you to react•your reaction time - the longer your reaction time, the longer you thinking distance

125

Braking distance is affected by...

•Your speed - for a given braking force, the faster a vehicle travels, the longer it takes to stop•Weather or road surface - if it’s wet or icy, or there are leaves or oil on the road, there is less grip(so less friction), can causes tyres to skid •Condition of tyres - if bald, they can’t get rid of water in wet conditions = skidding•How good your brakes are - if worn or faulty, they won’t apply as much force

126

When the brake is pushed, this causes brake pads to be pressed onto the wheels...

Contact force = friction, which causes work to be done.

127

The work done between the brakes and the wheels transfer energy from the kinetic energy stores of the wheels...

To the thermal energy stores of the brakes. The brakes increase in temperature.

128

The faster a vehicle is going, the more energy it has in its kinetic stores...

So the more work needs to be done to stop it. This means that the greater braking force is needed to make it stop within a certain distance

129

A larger braking force means...

A larger deceleration

130

Very large deceleration can be dangerous because...

They may cause brakes to overheat (they don’t work as well) or could cause the vehicle to skid

131

Estimate the forces involved in accelerations if vehicles by...

Using typical values

132

Momentum(kg m/s)...

Mass(kg)x velocity(m/s) P=m x v

133

Momentum is...

A property that all moving objects have

134

The greater the mass of an object, or the greater its velocity...

The more momentum the object has

135

In a closed system the total momentum before an event (e.g a collision)...

Is the same after the event. This is called conservation of momentum

136

A closed system...

Is the fancy was of saying that no external forces act

137

If the momentum before an event is zero, the momentum after will be zero...

E.G:In an explosion, the momentum before is zero. After the explosion, the pieces fly off in different directions, so that the total momentum cancels out to zero

138

A moving car hits into the back of a parked car. The crash causes the two cars to lock together, and they continue moving in the direction that the original moving car was travelling at, but at a lower velocity...

Before: The momentum was equal to mass of moving car x it’s velocity After: The mass of the moving object has increased, but it’s momentum is equal to the momentum before the collision. So an increase in mass causes a decrease in velocity