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Physics > Topic 5 - Forces > Flashcards

Topic 5 - Forces Flashcards

1
Q

What two qualities do vectors have? Name 2 vectors.

A

Magnitude and direction. Velocity, momentum, force etc.

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2
Q

What qualities do scalars have? Name two scalars.

A

Scalars have only magnitude and no direction. Mass, speed, time etc.

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3
Q

What is the difference between a contact and a non contact force?

A

A contact force needs to be touching something to have an effect. A non-contact force can perform a push or pull without touching something.

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4
Q

What is an interacting pair and which of Newton’s laws is this equivalent to?

A

An interacting pair is a pair of equal and opposite forces acting on two interacting objects. This is Newton’s third law.

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5
Q

What is gravitational force and what 2 ways does it affect objects?

A

Gravitational force is the force of attraction between masses. It affects us because the planet has a gravitational force which makes things fall to the ground and it also gives objects a mass.

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6
Q

What is the difference between weight and mass?

A

Mass is the amount of ‘stuff’ in an object, whereas weight is the force of gravity acting upon an object.

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7
Q

What unit is and how is weight measured? What unit is mass measured in?

A

Weight is measured in newtons using a spring newtonmeter. Mass is measured in kilograms.

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8
Q

What is the equation linking mass, weight and gravitational field strength?

A

Weight = mass x gravitational field strength
Weight is in N
Mass is in Kg
Gravitational field strength is in N/Kg

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9
Q

Are weight and mass directly proportional? How can you write this?

A

They are. It is written as W(directly proportional sign)m

The directly proportional sign looks like an infinity symbol with a chunk missing from the right.

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10
Q

What is a free body diagram and what does it show?

A

A free body diagram is a diagram showing the forces acting on and around an object. The size of the arrows shows the size of the forces.

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11
Q

What is a resultant force?

A

It is a single force acting on an object, determined by adding forces in the same direction and taking away forces acting in the opposite direction (for example).

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12
Q

What happens when a force moves through object at a distance and what is the equation you can use to find this out?

A

Energy is transferred and work is done. You can find out what work has been done through the equation W=Fs.
W is work done in Joules
F is force in N
s is distance in m

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13
Q

How would you use a scale drawing to find the resultant force?

A

First you would draw the forces. Then draw a straight line from the start of the first force to the end of the last one (the resultant force). Finally, measure this distance to find the magnitude and angle of the force.

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14
Q

What is an equilibrium?

A

Where the resultant force acting on an object is 0.

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15
Q

How do you resolve a force?

A

Draw it on a scale grid to scale, and then work it out the same way you would work out the gradient on a graph.

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16
Q

What does it mean if an object is elastically deformed? What energy stores is the energy converted to?

A

If it is elastically deformed, it can go back to its original shape after being stretched. This makes it an elastic object. When work is done on it, all of the energy is transferred to the elastic potential energy store.

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17
Q

What does it mean if an object is inelastically deformed?

A

It means that it can’t go back to its original shape after it has been stretched.

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18
Q

What equation shows that extension is directly proportional to force?

A

F = ke
F is force in N
K is spring constant in N/m
E is extension in m

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19
Q

What is the limit of proportionality?

A

It is where an object stops being elastically deformed and becomes inelastically deformed. On an extension/force graph this is where the graph curves off.

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20
Q

What is a moment?

A

A turning effect of a force, causing an object to rotate.

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21
Q

How is a moment calculated?

A

M = Fd
M is moment in Nm
F is force in N
d is distance in m

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22
Q

How is the force of a moment on a spanner most effective?

A

When it is applied perpendicular to the object. Other angles make a smaller distance, thus a smaller moment.

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23
Q

How is an object balanced about a pivot?

A

When the clockwise and anti-clockwise forces are equal.

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24
Q

How do levers make applying work easier?

A

They increase the distance between the pivot and the force applied. Using the equation, this means that you need less force to get the same effect.

25
Q

Why will a larger gear cause a larger moment? Do large gears move faster or slower than small gears?

A

Because the distance to the pivot is greater. They move slower.

26
Q

What is the equation for calculating the pressure of the surface of a fluid?

A

P = F/A
P is pressure in Pa
F is force normal (at a right angle) to the surface in N
A is surface area in m squared

27
Q

If an object is more dense, does it have more or less particles in a space? In a liquid, how does density change as it gets deeper?

A

It has more particles. As you get deeper into a liquid, the density increases because there are more particles above it.

28
Q

What is the equation for pressure in a liquid using density?

A 
P = hρg
P is pressure in Pa
H is height in m
ρ is density in kg/m cubed
G is gravitational field strength in N/kg
29
Q

Why does upthrust occur? How large is the force of upthrust?

A

Upthrust occurs because when an object is submerged in a liquid pressure acts on it in all directions, and as you get deeper this increases, meaning there is a larger force at the bottom than the top of the object. This creates the resultant force upthrust, which is equal to the size of the submerged object.

30
Q

What is the relationship with weight to upthrust?

A

If an object floats, the upthrust is equal to the weight. If an object sinks, the upthrust is less than the weight.

31
Q

What is the relationship between density, weight and upthrust?

A

A less dense object displaces it’s volume (equivalent to the same weight of water) before the whole object is submerged, meaning upthrust keeps it floating. A more dense object displaces it’s volume when it is fully submerged, so upthrust can’t keep it floating and it sinks.

32
Q

How is atmospheric pressure created and as you get further from earth does it increase or decrease?

A

It is created by air particles colliding with surfaces. As you get further from Earth this pressure decreases because it is less dense and there are less surfaces to collide with. There are also less air particles at high altitudes so the weight behind it decreases so there is less pressure.

33
Q

Why is distance scalar and displacement a vector?

A

Distance only has magnitude. Displacement also measures the direction in a straight line from the finish to end points. Therefore, if you walk one step west and one east, the displacement is 0 steps but the distance is 2 steps.

34
Q

Give the formula for calculating a constant speed or an average speed.

A

S = vt
S is distance travelled in m
v is speed in m/s
t is time in seconds

35
Q

How can an object have a constant speed with a changing velocity?

A

The object changed direction whilst travelling at the same speed, such as travelling at 2m/s in a circle.

36
Q

What are the 6 speeds you need to know?

A 
Walking: 1.5m/s
Running: 3m/s
Cycling: 6m/s
Car: 25m/s
Train: 55m/s
Plane: 250m/s
37
Q

What is acceleration?

A

The change in velocity in a certain amount of time.

38
Q

What is the equation for acceleration?

A

A = ΔV / t
A is acceleration in m/s squared
ΔV is change in velocity in m/s
t is time in s

39
Q

What is uniform acceleration?

A

Constant acceleration.

40
Q

What is the equation for uniform acceleration?

A 
V squared - u squared = 2as
V is final velocity in m/s
U is initial velocity in m/s
A is acceleration in m/s squared
S is distance in m
41
Q

What is drag?

A

The force of friction in a liquid or gas or on a solid.

42
Q

Will a car have to do more or less work against drag as it speeds up?

A

More. Drag increases with speed, so the car has to work faster to get to a steady speed.

43
Q

What is terminal velocity?

A

When an object falls, it speeds up because gravity is greater than the friction acting against it. Eventually speed increases and drag increases, so the force of friction becomes equal to the acceleration, creating 0 resultant forces and meaning the object has reached the fastest speed it will fall, or its terminal velocity.

44
Q

What factors does terminal velocity rely on?

A

Air resistance.
Drag vs weight.
The shape and area of the object. An example is a skydiver falling and then increasing their area so that W = mg but the terminal velocity is much slower.

45
Q

What is Newton’s First Law?

A

A resultant force is needed to slow something down, start it or speed it up.
“A resultant force of 0 on a stationary object means it won’t move. A resultant force of 0 on a moving object will mean it keeps going at a constant velocity.”

46
Q

What is Newton’s Second Law?

A

Resultant force is directly proportional to acceleration.

47
Q

What is the formula for Newton’s Second Law?

A

F = ma
F = resultant force in N
M is mass in kg
A is acceleration in m/s squared

48
Q

What is Newton’s Third Law?

A

When two objects interact, the forces exerted on each other are equal and opposite.

49
Q

What is inertia and how is it calculated?

A

Inertia is the tendency to continue at the same state of motion, like in Newton’s First Law. It’s calculated with the ratio of force over acceleration.

50
Q

What is the stopping distance?

A

Stopping distance = thinking distance + braking distance.

51
Q

What factors affect thinking distance?

A

Speed and reaction time.

52
Q

What factors affect braking distance and what is the average braking speed?

A

Factors are speed, road surface, tyre condition and brake condition. The average braking speed is 14m at 30mph, 55m at 60mph and 75m at 70mph.

53
Q

How does a car brake work?

A

Brake pads are pressed against the wheels, creating friction and causing work to be done, meaning the kinetic energy goes to the thermal energy store and the wheels heat up. A faster vehicle needs more braking time and this fast deceleration can be dangerous because it can cause skidding and can damage the tires.

54
Q

What is the typical reaction time and what can affect it?

A

It is between 0.2 and 0.9 seconds and can be affected by drinking alcohol, tiredness, distractions and drugs.

55
Q

Why does the speed of a car affect the braking distance more than the thinking distance?

A

Because as the car speeds up, the brakes will be the same as the car’s kinetic energy, meaning as speed increases kinetic energy increases four-fold. This means the braking distance needed increases by four-fold.

56
Q

What is the equation for momentum?

A

P = mv
P is momentum in kg m/s
M is mass in kg
V is velocity in m/s

57
Q

What is the conservation of momentum?

A

The conservation of momentum means the momentum stays the same before and after an object has moved in a closed system. If momentum before an event is 0, momentum after an event will be 0 because momentum in different directions cancel out.

58
Q

Give the equation that forces cause a change in momentum.

A

F = mΔv / Δt
F is force in N
MΔv is change in momentum in kg m/s
Δt is change in time in s

Physics (10 decks)

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