Forces - paper 2 Flashcards

To revise forces (Paper 2)

1
Q

Define a scalar

A

A quantity that only has magnitude.

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2
Q

Give some examples of scalar quantities

A

Speed, distance, time, mass, volume

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3
Q

Define a vector quantity

A

A quantity that has magnitude and direction.

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4
Q

Give some examples of vector quantities

A

Velocity, displacement, acceleration, momentum, any force

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5
Q

State some examples of non contact forces

A

Friction, air resistance, drag, upthrust, tension, normal contact force

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6
Q

State some examples of contact forces

A

Gravity, magnetism, electrostatic

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7
Q

State the equation with all units for Weight

A

weight (N) = mass (kg) × gravitational field strength(N/kg)

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8
Q

What is the mathematical relationship between weight and mass.

A

They are directly proportional

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9
Q

What equipment can be used to measure weight?

A

Weight is measured using a calibrated spring-balance called a newtonmeter

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10
Q

Define a resultant force

A

When 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.

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11
Q

When is work done?

A

When a force causes an object to move through a distance

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12
Q

What is the relationship between work done and energy transferred

A

Work done = energy transferred

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13
Q

State the equation and all units for work done

A

work done (J) = force (N) × distance moved along the line of action of the force (m)

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14
Q

Define 1 joule of work

A

One joule of work is done when a force of one newton causes a
displacement of one metre. 1 joule = 1 newton-metre

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15
Q

State Hooke’s law

A

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.

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16
Q

State Hookes law equation with all units

A

force (N) = spring constant (N/m) × extension (m)

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17
Q

When an object is stretched or squared what form of energy does it store?

A

Elastic potential energy.

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18
Q

Define elastic deformation

A

When the forces are removed the object returns to its original length

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19
Q

Define inelastic deformation

A

When the forces are removed the object doesn’t returns to its original length, it stays permanently stretched.

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20
Q

Define a moment

A

The turning effect of a force

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21
Q

State the equation for a moment, with all units

A

moment of a force (Nm) = force (N) × perpendicular distance (m)

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22
Q

If an object is balanced what can you say about the clockwise and anticlockwise moments

A

They must be equal

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23
Q

Define a liquid

A

Either a liquid or gas, particles must be able to move past each other

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24
Q

State the equation for pressure with all units

A

pressure = force / area
Pressure - Pa
Force - N
Area - m2

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25
What is the relationship between pressure from a liquid and depth
As depth increases pressure increase due to a greater number of particles and force pushing on the object.
26
How does liquid pressure cause upthrust?
A partially (or totally) submerged object experiences a greater pressure on the bottom surface than on the top surface, (pressure increases with depth). This creates a resultant force upwards. This force is called the upthrust.
27
Define the atmosphere
The atmosphere is a thin layer (relative to the size of the Earth) of air round the Earth.
28
State the relationship between altitude and the density of the atmosphere
he atmosphere gets less dense with increasing altitude.
29
As altitude increase why does atmospheric pressure decrease?
Air molecules colliding with a surface create atmospheric pressure. 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.
30
State the difference between distance and displacement
Distance is a scalar - doesn't involve direction Displacement is a vector and is measured in a straight line from the start point to the finish point and the direction of that straight line.
31
State the difference between speed and velocity
Speed is a scalar | Velocity is a vector
32
``` State the following typical speeds: walking Running Cycling Sound ```
walking - 1.5 m/s Running - 3.0 m/s Cycling - 6.0 m/s Sound - 330 m/s
33
State the equation with all units to calculate speed
distance (m) = speed (m/s) × time (s)
34
how can speed be calculated from a distance - time graph
Using the gradient
35
State the equation to calculate average acceleration, with all units
acceleration = change in velocity / time acceleration - m/s2 velocity - m/s time - s
36
How can acceleration be found from a velocity - time graph
From the gradient
37
How can displacement be found from a velocity - time graph
From the area under the line
38
What is the initial rate of acceleration for an object falling close to the earths surface?
9.8 m/s2
39
What is terminal velocity and when does it occur?
the maximum velocity an object can fall at, this happens when forces are balanced
40
What factors can increase the size of air resistance
Speed Surface area Density of the fluid which the object is falling through
41
State Newtons first law
if the resultant force acting on an object is zero the object will stay at rest or move at a constant velocity
42
The tendency of objects to continue in their state of rest or of uniform motion is called?
Inertia
43
State Newtons second law
The acceleration of an object is proportional to the resultant force acting on the object, and inversely proportional to the mass of the object.
44
State the equation with all units for Newtons Second law
resultant force (N) = mass (kg) × acceleration (m/s2)
45
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.
46
State Newton's third law
Whenever two objects interact, the forces they exert on each other are equal and opposite.
47
Define stopping distance
The stopping distance of a vehicle is the sum of the distance the vehicle travels during the driver’s reaction time (thinking distance) and the distance it travels under the braking force (braking distance).
48
Define thinking distance
the distance the car travels whilst a driver reacts to a situation
49
Define braking distance
the distance the car travels whilst the brakes are applied
50
State the typical reaction times for a human
0.2 s to 0.9 s.
51
State some factors that can affect a persons reaction times
tiredness, ages, drugs and alcohol, Distractions
52
State some factors that can affect the braking distance of a car
Rain, ice, snow, poor quality brakes, poor quality tyres, gradient of the road, mass of the car
53
State the one factor that can increase both the thinking distance and braking distance
Speed
54
State the equation for momentum
momentum = mass × velocity
55
State the units for momentum
kg m/s
56
Define the conservation of momentum
In a closed system, the total momentum before an event is equal to the total momentum after the event.
57
What is required to change the momentum of an object
A force
58
explain safety features such as: air bags, seat belts, gymnasium crash mats, cycle helmets and cushioned surfaces for playgrounds with reference to the concept of rate of change of momentum.
A air bag increases the time for a person to stop. Therefore for the same change of momentum a smaller force can be used. Force = change in momentum/time
59
Define acceleration
when an object speeds up, slows down or changes direction.
60
Units of force
Newtons (N)
61
What is the centre of mass of an object?
The point at which the mass may be thought to be concentrated
62
Where does the centre of mass lie in symmetrical objects?
Along the line of symmetry
63
How can the centre of mass of an irregular shape be found?
by hanging the shape from a point and a plumb line is used to draw a vertical line downwards from the pivot. this is repeated from different points Where the lines meet is the centre of mass
64
What is a gear?
A rotating machine with cogs that mesh with another toothed part to transmit a moment
65
What do gears act as?
A force multiplier