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physics. > Forces > Flashcards

Forces Flashcards

1
Q

What are scalar quantities?

A

Only have one magnitude and no direction.

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2
Q

What are the examples of scalar quantities?

A 
> speed.
> distance.
> temperature.
> mass.
> time.
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3
Q

What are vector quantities?

A

Have a magnitude and a direction.

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4
Q

What are the examples of vector quantities?

A 
> force.
> displacement.
> momentum.
> velocity.
> acceleration.
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5
Q

What is meant by the term “force” in physics?

A

A push or pull on an object caused by it interacting with something.

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6
Q

What are the two types of forces?

A

> contact forces.

> non-contact forces.

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7
Q

What are contact forces?

A

Where objects have to be touching.

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8
Q

What are non-contact forces?

A

Where objects don’t need to be touching.

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9
Q

What are some examples of contact forces?

A

> friction.
tension.
air resistance.
normal contact force.

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10
Q

What are some examples of non-contact forces?

A

> electrostatic force.
gravitational force.
magnetic force.

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11
Q

What is meant by the term “weight” in physics?

A

Force that acts on an object due to gravity.

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12
Q

What is the formulae for weight?

A

weight = mass x gravitational field strength
w = m g
N kg N/kg

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13
Q

What is the centre of mass?

A

Point at which an object’s weight appears to act.

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14
Q

What is a free body diagram?

A

Shows all forces acting on an isolated object.

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15
Q

What is an equilibrium?

A

When the forces acting on an object are balanced and the resultant force is zero.

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16
Q

What is a resultant force?

A

A single force that can replace all the forces acting on an object to give the same effect as all the original forces acting together.

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17
Q

What are the two ways of calculating resultant force?

A

1)
> add forces pointing in same direction.
> subtract forces pointing in opposite directions.
> F₁ - F₂ = resultant force.

2)
> draw forces to scale and tip-to-tail.
> measure length of resultant force to find its magnitude and angle to find its direction.

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18
Q

What is work done?

A

When a force moves an object from one point to another, energy is transferred and work is done on the object.

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19
Q

What is the formulae for work done?

A

work done = force x distance
w = f x s
J N M

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20
Q

How can a stationary object change its shape?

A

When more than one force act on it.

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21
Q

What are the two types of deformation?

A

> elastic.

> inelastic.

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22
Q

What is the elastic type of deformation?

A

Where an object goes back to its original shape and length after forces have been removed.

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23
Q

What is the inelastic type of deformation?

A

Where an object doesn’t go back to its original shape and length after forces have been removed.

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24
Q

What is the formulae for force?

A

force = spring constant x extension/compression
F = k x e
N N/m m

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25
What is distance?
How far an object has moved. [scalar] [not including its direction]
26
What is displacement?
The distance and the direction in a straight line from an object's starting point to its finishing point. [vector]
27
What is speed?
How fast you're going with no regard to direction. | [scalar]
28
What is the formulae for distance travelled?
distance travelled = speed x time s = v x t m m/s s
29
What are the factors that can affect a person's walking, running and cycling speed?
> ability. > age. > distance travelled. > type of ground.
30
What is velocity?
The speed in a certain direction. | [vector]
31
What happens to an objects velocity if they are moving in a circular motion with a constant speed?
The velocity changes.
32
What is acceleration?
The change in velocity in a certain amount of time.
33
What is the formulae for acceleration?
acceleration = change in velocity ÷ time a = ∆v ÷ t m/s² m/s s
34
What is deceleration?
Negative acceleration which shows an object is slowing down.
35
What is Newton's first law?
> if zero resultant force acts on stationary object, the object doesn't move. > if zero resultant force acts on moving object, it continues moving at same velocity. > if non-zero resultant force acts on an object, the object accelerates.
36
What is inertia?
The tendency of an object to continue in. the same state of motion.
37
What is Newton's second law?
> acceleration is directly proportional to resultant force. ↳ F ∝ a. > acceleration is inversely proportional to mass.
38
What is the formulae for resultant force?
resultant force = mass x acceleration F = m x a N kg m/s²
39
What is inertial mass?
Measure of how hard it is to change an object's velocity. | Its the ratio of force over acceleration: m = F ÷ a.
40
What is Newton's third law?
Two interacting objects exert equal and opposite forces on each other.
41
What is an example of Newton's third law?
1) > rocket exhaust gas pushed downwards by rocket. ↳ causes equal and opposite force as gas pushes back on rocket. ↳rocket moves when upwards than rocket's weight. 2) > girl pushes on wall. ↳ equilibrium - wall pushes back on girl with equal and opposite force.
42
What is friction?
A force that acts to oppose an object's motion. It always acts in the opposite direction to movement.
43
What is drag?
The frictional force caused by any fluid on a moving object. | [e.g. air resistance]
44
What is the process of reaching terminal velocity?
force of gravity greater than frictional force ⟶ object acceleration ⟶ speed increases so friction increases ⟶ frictional force = force of gravity ⟶ resultant force is zero ⟶ terminal velocity reached.
45
What are the three factors that affect reaction times?
> tiredness. > drugs. > alcohol.
46
What are the steps to investigate reaction time?
> get someone to hold ruler so zero is between your thumb and forefingers. ↳ ruler dropped without warning and caught as fast as possible. ↳ use distance ruler fell to calculate reaction time.
47
What is the formulae to find stopping distance?
stopping distance = thinking distance + braking distance
48
What is thinking distance?
How far a vehicle moves during driver's reaction time.
49
What is braking distance?
Distance taken to stop whilst brakes are applied.
50
What are the two factors that increase thinking distance?
> faster vehicle speed. | > slow driver reaction times.
51
What are the four factors that increase braking distance?
> faster vehicle speed. > wet or icy weather. > poor road surface. > damaged or worn brakes or tyres.
52
What is the work done when stopping?
> driver brakes causing brake pads to be pressed onto wheels. ↳ friction between them causes work to be done. ↳ energy transferred from kinetic energy stores of wheels to thermal energy stores of brakes. ↳ brakes heat up.
53
What can large deceleration cause?
> brakes to overheat. | > vehicle to skid.
54
What is the formulae for momentum?
momentum = mass x velocity p = m x v kg m/s kg m/s
55
How is momentum affected by mass and velocity?
> the greater an object's mass, the greater its momentum. | > the greater an objects velocity, the greater its momentum.
56
What is the transfer between joule and newton-metre?
1 joule = 1 newton-metre.
56
What is the typical value for walking, running and cycling?
> walking = 1.5 m/s > running = 3 m/s > cycling = 6 m/s
57
What is the equation for uniform acceleration?
(final velocity)² - (initial velocity)² = 2 x acceleration x distance v² - u² = 2 x a x s m/s m/s m/s² m
58
What is the formulae to calculate the work done in stretching or compressing a spring?
elastic potential energy = 0.5 x spring constant x (extension)² Eℯ = 1/2 x k x e
59
What state of matter is a fluid?
It can either be a liquid or gas.
60
What is the formulae to calculate the pressure at the surface of a fluid?
pressure = force normal to a surface / area of that surface p = F / A PA N m²
61
What is the formulae to calculate the pressure due to a column of liquid?
pressure = height of the column x density of the liquid x gravitational field strength p = h x 𝛒 x g PA m kg/m³ N/kg
61
What is the formulae to calculate the pressure due to a column of liquid?
pressure = height of the column x density of the liquid x gravitational field strength p = h x 𝛒 x g PA m kg/m³ N/kg
62
What is the force called upthrust?
When a partially (or totally) submerged object experiences a greater pressure on the bottom surface than on the top surface which creates a resultant force upwards.
63
What is the atmosphere?
A thin layer (relative to the size of the Earth) of air round the Earth.
64
What happens to the atmosphere where there is an increasing altitude?
It gets less dense.
65
How is atmospheric pressure created?
When air molecules collide with a surface.
66
What happens to the atmospheric pressure as there is an increase in height?
It decreases.
67
Why does the atmospheric pressure decrease with an increase in height?
The number of air molecules 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.
68
What happens when force is applied to the brakes of a vehicle?
Work is done by friction force between the brakes and the wheel reduces the kinetic energy of the vehicle increasing the temperature of the brakes.
69
The greater the speed of a vehicle...
...the greater the breaking force needed to stop the vehicle in a certain distance.
70
The greater the braking force...
...the greater the deceleration of the vehicle.
71
Why are large decelerations dangerous?
It may lead to brakes overheating and/or loss of control.
72
What is the conservation of momentum?
When in a closed system, the total momentum before an event is equal to the total momentum after the event.
73
Why are cars designed to slow people down over a longer time when they have a crash?
The longer it takes for a change in momentum, the smaller the rate of change of momentum and so the smaller the force.
74
Why are seat belts used as a safety feature?
They stretch slightly increasing the time taken for the wearer to stop.
75
Why are air bags used as a safety feature?
They inflate before you hit the dashboard of a car. The compressing air inside slows you down more gradually.
76
Why are gymnasium crash mats/cushioned playground flooring used as a safety feature?
They increase the time taken for you to stop if you fall on them.
77
Why are cycle helmets used as a safety feature?
They contain a crushable layer of foam which helps to lengthen the time taken for your head to stop in a crash reducing the impact on your brain.

physics. (10 decks)

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