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physics > topic 5 - forces > Flashcards

topic 5 - forces Flashcards

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AP® Physics flashcards Physics 101 flashcards
1
Q

What is a scalar quantity?

A

A quantity that only has a magnitude

A quantity that isn’t direction
dependent

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2
Q

What is a vector quantity?

A

A quantity that has both a magnitude and an associated direction.

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3
Q

How can a vector quantity be drawn and
what does it show?

A

As an arrow

The length of the arrow represents the magnitude

The arrow points in the associated direction

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4
Q

What is a force?

A

A push or pull acting on an object due to an interaction with another object.

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5
Q

What are the two categories that all
forces can be split into?

A
  1. Contact forces (objects touching)
  2. Non-contact forces (objects separated)
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6
Q

Give three examples of contact forces.

A

Friction
Air resistance
Tension

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7
Q

Give three examples of non-contact forces.

A
  1. Gravitational forces
  2. Electrostatic forces
  3. Magnetic forces
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8
Q

Is force a vector or a scalar quantity?

A

Vector

It has both a magnitude and an
associated direction

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9
Q

Give three examples of vector quantities

A
  1. Velocity
  2. Displacement
  3. Force
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10
Q

Give three examples of scalar quantities.

A

● Temperature
● Time
● Mass
● Speed
● Distance
● Energy

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11
Q

What is weight?

A

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

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12
Q

What quantities does weight depend on?

A

The object’s mass

The gravitational field strength at the given position in the field

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13
Q

What is meant by an object’s centre of mass?

A

The single point where an object’s
weight can be considered to act through.

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14
Q

What is the name given to the single force that is equivalent to all the other forces acting on a given object?

A

the resultant force

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15
Q

What does it mean if a force is said to do
‘work’?

A

The force causes an object to be
displaced through a distance.

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16
Q

What distance must be used when calculating work done?

A

It must be the distance that is moved
along the line of action of the force.

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17
Q

Under what circumstance is 1 joule of
work done?

A

When a force of 1 Newton causes a
displacement of 1 metre.

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18
Q

How many Newton-metres are equal to 1
joule of energy?

A

1 Nm = 1 J

19
Q

What occurs when work is done against
frictional forces?

A

● A rise in temperature of the object
occurs
● Kinetic energy is converted to heat

20
Q

Why does air resistance slow down a projectile?

A

● The object does work against the air
resistance
● Kinetic energy is converted in to heat,
slowing down the object

21
Q

Explain the relationship between the
force applied and the extension of an
elastic object.

A

The extension is directly proportional to
the force applied, provided that the limit
of proportionality is not exceeded.

22
Q

What is meant by an inelastic (plastic)
deformation?

A

● A deformation which results in the
object being permanently stretched
● The object doesn’t return to its original
shape when the force is removed

23
Q

What type of energy is stored in a spring
when it is stretched?

A

Elastic potential energy

24
Q

What can extension be replaced with in
the equation for spring force?

A

Compression

25
Q

what is a moment

A

the turning effect of a force

26
Q

What distance measurement is used when calculating a moment?

A

The perpendicular distance from the
pivot to the line of action of the force.

27
Q

If an object is in equilibrium, what can be
said about the moments acting on the
object?

A

The clockwise moments are equal to the
anticlockwise moments.

28
Q

What three parts make up a lever
system?

A
  1. Load
  2. Effort
  3. Pivot
29
Q

How can a lever be used as a force multiplier?

A

If the distance between the effort and pivot is
greater than the distance between the pivot
and load, the force applied on the load is
greater than the effort force. This is since the moment on both the effort and load must be the same.

30
Q

Give an example of when a lever may be used to
multiply a force.

A

A wrench, which has a long handle so that the
force applied by the user is multiplied.

31
Q

What determines the moment of a gear
wheel?

A

The size of the wheel

32
Q

Describe the moment and speed of a larger gear being driven by a smaller
gear.

A

The larger wheel will rotate more slowly but
will also produce a larger moment.

33
Q

What is meant by the term ‘fluid’?

A

A liquid or a gas.

34
Q

In any fluid, at what angle do the forces
due to pressure act on a given surface?

A

At right angles (normal to) the surface.

35
Q

What happens to the density of the atmosphere with increasing altitude?

A

The atmosphere becomes less dense as altitude increases.

36
Q

Explain why atmospheric pressure decreases with an increase in height.

A

● Pressure is created by collisions of air
molecules
● The quantity of molecules (and so weight)
decreases as the height increases
● This means atmospheric pressure decreases
with an increase of height

37
Q

What is the Earth’s atmosphere?

A

A thin (relative to the magnitude of the Earth) layer of gas surrounding the Earth.

38
Q

How does pressure in fluids increase with depth?

A

As the depth increases, the mass of liquid above that depth also increases.
This means that the force due to the mass increases.
Since the force has increased whilst the area has remained constant, the pressure will
increase

39
Q

Why does pressure in fluids increase
with density?

A

As the density of a fluid increases, the number of
particles in a given volume increases.
Consequently the weight of the fluid is greater.
This means that the force from the fluid above a
certain point is larger. Since the force has
increased, the pressure also increases.

40
Q

Why are objects in a fluid subject to upthrust

A

When an object is submerged in a fluid, it has a
higher pressure below it than it does above, as there
is more weight above it at the bottom than there is at
the top. This leads to an upwards force called
upthrust.

41
Q

why do you float

A

upthrust is more than weight

42
Q

What is upthrust always equal to?

A

The weight of the fluid that the object
displaces.

43
Q

What factors influence whether an object
will sink or float?

A

● Upthrust
● Weight
● Density of fluid

44
Q

Explain why an object with a density
greater than that of water can never
float.

A

Upthrust is equal to the weight of the displaced
fluid. If the density of the object is high, there
would not be enough volume displaced to
produce an upthrust larger than the object’s
weight. This means that it will sink.

physics (8 decks)

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