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Physics > Motions And Forces > Flashcards

Motions And Forces Flashcards

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1
Q

Scalar quantity

A

Only has magnitude
Isn’t direction dependent

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2
Q

Vector quantity

A

Both magnitude and an associated direction

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3
Q

How can a vector quantity be represented

A

Using vector arrows

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4
Q

How do vector arrows represent vectors

A

The length of arrow represents magnitude

Arrow points in associated direction

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5
Q

Three examples of vector quantities

A
  1. Velocity
  2. Displacement
  3. Force
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6
Q

Examples of scalar quantities

A

Temperature
Speed
Mass
Time
Distance
Energy

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7
Q

What is velocity

A

Speed of an object in a specific direction

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8
Q

Equation relating average speed, distance and time

A

Average speed = distance / time

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9
Q

On a distance time graph what value does the gradient of the line represent

A

Speed

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10
Q

On a displacement time graph what value does the gradient of the line represent

A

Velocity

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11
Q

What must be done to calculate the speed at a given time from a distance time graph from an accelerating object

A

Draw a tangent to the curve at the required time
Calculate the gradient of the tangent

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12
Q

State equation for the average acceleration of an object

A

Acceleration (m/s^2) = change in velocity (m/s) / time taken (s)

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13
Q

How can the distance travelled by an object be calculated from a velocity time graph

A

It is equal to the area under the graph

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14
Q

On a velocity time graph what does the gradient of the graph represent

A

Acceleration

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15
Q

Typical value for speed of sound

A

330 m/s

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16
Q

Typical value for human walking speed

A

1.5 m/s

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17
Q

Typical value for human running speed

A

3 m/s

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18
Q

Typical value for human cycling speed

A

6 m/s

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19
Q

Approximate value for the acceleration of an object in free fall under gravity near the earths surface

A

10 m/s^2

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20
Q

Name given to the single force that is equivalent to all the other forces acting on a given object

A

Resultant force

21
Q

Newton’s first law for a stationary object

A

If the resultant force on a stationary object is zero, the object will remain at rest

22
Q

Newton’s first law for a moving object

A

If the resultant force on a moving object is zero, the object will remain at constant velocity (same speed in same direction)

23
Q

Defining equation for Newton’s second law

A

Resultant force = mass x acceleration

F = ma

24
Q

Newton’s second law in words

A

An objects acceleration is directly proportional to the resultant force acting on it and inversely proportional to its mass

25
Q

What is weight

A

The force that acts on an object due to gravity and the objects mass

26
Q

What quantities does weight depend on

A

Weight = mass x gravitation field strength

Objects mass
Gravitations field strength at the given position in the field

27
Q

Unit for weight

A

Newton

28
Q

Unit for gravitational field strength

A

N/kg

29
Q

What price of equipment can be used to measure an objects weight

A

A calibrated spring balance or newton meter

30
Q

When can an object travelling at a constant speed not have a constant velocity

A

When the object is changing direction

E.g moving in a circle

31
Q

Why does an object travelling at a constant speed in a circle not have a constant velocity

A

Speed is a scalar quantity
Velocity is a vector quantity which means it can only be constant if the direction is constant
In a circular motion the direction is continuously changing
Velocity is constantly changing

32
Q

What is the resultant force that acts on an object moving in a circle called and in which directions does it act

A

Called the centripetal force and acts towards the centre of the circle

33
Q

What is inertial mass

A

A measure of how difficult it is to change a give objects velocity

The ration of force over acceleration

34
Q

State Newton’s third law

A

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

35
Q

State the equation used to calculate an objects momentum

A

Momentum = mass x velocity

36
Q

What is the unit for momentum

A

kgm/s

Kilogram metres per second

37
Q

In a closed system, what can be said about the momentum before and after collision

A

The total momentum before and after are equal

38
Q

State an equation linking change in momentum, force and time

A

Force x time = change in momentum

39
Q

How can you measure human reaction times

A

Using ruler drop test
Person A and B hold each end of ruler with 0cm mark at the bottom
Pardon A drops ruler without telling B
Person B catches is
Distance travelled corresponds to their reaction time

40
Q

Why is it important the 0cm mark is at the bottom when doing the ruler test

A

So you can obtain the distance without having to calculate it

41
Q

What is the stopping distance if a vehicle equal to

A

The sum of thinking distance and braking distance

42
Q

For a given braking distance, if the vehicles speed is increased, what can be said about its stopping distance

A

The stopping distance is increased with an increase in speed

43
Q

Give a typical range of values for human reaction time

A

0.2 - 0.9 seconds

44
Q

Give three factors which can affect a drivers reaction time

A

Tiredness
Drugs
Alcohol

45
Q

Give two factors which may affect braking distance

A

Adverse (wet/icy) road conditions
Poor tyre or brake conditions

46
Q

Describe the energy transfers that take place when a car applies its brakes

A

Work is done by the friction force between the brakes and wheel
Kinetic energy of the wheel is converted to heat and is dissipated to the surroundings through brake discs

47
Q

To stop a car in a given distance, if it’s velocity is increased, what must happen to the braking force applied

A

Braking force must also be increased

48
Q

State two consequences of a vehicle undergoing very large decelerations

A

Kinetic energy converted to heat is very high causing brakes to overheat
Loss of control of the vehicle

Physics (5 decks)

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