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Physics GCSE > Forces and Motion > Flashcards

Forces and Motion Flashcards

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1
Q

What is a force?

A

A push or a pull that acts on an object due to the interaction with another object

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2
Q

What word is used to describe an object that is slowing down?

A

Decelerating

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3
Q

Give two examples of a non-contact force

A

E.g. gravitational force, electrostatic force, magnetic force

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4
Q

What is a free body force diagram?

A

A diagram showing all the forces acting on a single object only

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5
Q

What is meant by the term acceleration?

A

The rate of change of velocity

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6
Q

What is meant by the term “inertia”?

A

The tendency of objects to continue in their state of rest or of uniform motion

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7
Q

If an object is changing speed, how can instantaneous speed at a certain time be calculated from a distance-time graph?

A

Draw a tangent to the curve at that time and find the gradient of the tangent

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8
Q

How and why does the weight of an object change as it moves away from a planet and into deep space?

A

The weight decreases, as the gravitational field strength decreases

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9
Q

What do physicists mean by the term “weight”?

A

The force due to gravity acting on an object

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10
Q

What is meant by the term “inertial mass”?

A

A measure of how difficult it is to change the velocity of an object

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11
Q

Why does an object falling through a fluid accelerate then reach a terminal velocity?

A

The object initially accelerates due to the force of gravity. As it accelerates, the drag force increases, so the resultant force decreases. Eventually, the drag force is equal to the force of gravity, so the resultant force is zero

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12
Q

What is Newton’s Third Law of Motion?

A

When object A exerts a force on object B, object B exerts an equal and opposite force on object A

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13
Q

What is Newton’s Second Law of Motion?

A

The acceleration of an object is directly proportional to the resultant force acting on the object, and inversely proportional to the mass of the object (F = ma)

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14
Q

Compare speed and velocity for an object moving at a constant speed in a circle

A

The speed is constant. The velocity changes, because the direction changes

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15
Q

What is the acceleration of an object falling freely under gravity near the Earth’s surface?

A

9.8 m/s^2

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16
Q

What can you say about the resultant force on an object moving at terminal velocity?

A

Resultant force is zero

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17
Q

What are contact forces?

A

Forces exerted when the objects are physically touching

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17
Q

What equation links force, mass, and acceleration?

A

Resultant force = mass x acceleration
F = ma

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17
Q

What are non-contact forces?

A

Forces exerted when the objects are physically separated

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18
Q

What is meant by the term “resultant force”?

A

The one single force that can replace a number of forces and has the same effect as all the original forces acting together

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19
Q

How is weight calculated?

A

Weight = mass x gravitational field strength
W = mg

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20
Q

How is inertial mass defined?

A

Inertial mass = resultant force / acceleration

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21
Q

How is weight measured?

A

By using a calibrated spring balance e.g. a newtonmeter

22
Q

Give three examples of a contact force

A

E.g. friction, air resistance, tension, normal contact force, upthrust

23
Q

What is Newton’s First Law of Motion?

A

An object will remain at rest, or travelling at a constant velocity, unless a resultant force acts on the object

24
Q

What is the resultant force on an object moving at terminal velocity?

A

0 N

25
Q

When considering pairs of forces in Newton’s Third Law, what can you say about the forces?

A

They must be the same type of force, and act on different objects

26
Q

What is meant by the “centre of mass” of an object?

A

The single point where the weight of an object may be considered to act

27
Q

How can arrows represent vectors?

A

Length of the arrow indicates magnitude, direction of arrow indicates direction of vector

28
Q

What is meant by velocity?

A

The speed in a given direction

29
Q

What is a parallax error?

A

Error that occurs due to incorrect positioning of the eyes while taking a reading on a measuring scale

30
Q

What is the difference between linear and non-linear extensions?

A

For an extension vs force graph, a linear extension is a straight line through the origin; a non-linear extension is a curve

31
Q

What is the difference between elastic deformation and inelastic deformation?

A

For elastic deformation, the object returns to its original shape and size when the force is removed. For inelastic, the object does not return to its original shape and size

32
Q

What happens to a spring if it is stretched beyond the limit of proportionality?

A

The extension will not be directly proportional to force, and inelastic deformation will occur

33
Q

Under what circumstances in the elastic potential energy stored in a spring equal to the work done to stretch the spring?

A

When elastic deformation occurs

34
Q

How many forces are required to stretch or compress an object?

A

Two

35
Q

What equation links momentum, mass and velocity?

A

Momentum = mass x velocity
p = mv

36
Q

What equation links force, spring constant, and extension?

A

Force = spring constant x extension
F = ke

37
Q

What equation links force, mass, and acceleration?

A

Resultant force = mass x acceleration
F = ma

38
Q

Can the equation F = ke be used for springs being compressed?

A

Yes, ‘e’ would represent compression

39
Q

What is Hooke’s law?

A

The extension of an elastic object is directly proportional to the force applied provided that the limit of proportionality is not reached

40
Q

How do you calculate elastic potential energy?

A

elastic potential energy = 1/2 x spring constant x (extension)2
EEL = 1/2 ke2

41
Q

What is the equation that links resultant force, change in momentum and time?

A

Resultant force x time = change of momentum
F x t = m Δv

42
Q

What is resultant force (in terms of momentum)?

A

Rate of change of momentum

43
Q

What do safety features do?

A

Reduce the risk of injury in a collision

44
Q

What are examples of safety features?

A

seat belts
air bags
crash mats
bike helmets
shin pads
playground safety surfaces

45
Q

How do safety features prevent injury?

A

A resultant force is needed to change the momentum of an object.
To reduce the risk of injury, we need to make this resultant force as small as possible
We do this by increasing the time for which the force acts.
This decreases the rate of change of momentum
i.e. the RF is smaller

46
Q

Using ideas about momentum, explain why an egg thrown at a wall will smash, but an egg thrown at an open bed sheet does not smash. Assume the egg is thrown with the same velocity

A
  • As the egg is thrown with the same initial velocity, it always has the same initial momentum. When it impacts the surface, it comes to a rest, therefore the change in the momentum is always the same
  • Change in momentum = force x time
  • When the egg strikes the wall, it comes to a rest in a very small time. The rate of change of momentum is large. Therefore, the force acting on the egg is very large, which smashes the egg.
  • When the egg strikes the cloth, the time take to come to a rest is greatly increased
  • As the change in momentum of the egg is the same, an increase in the time means a decrease in the rate of change of momentum of the egg, so the force exerted on the egg is less
  • This force is small enough that the egg does not smash
47
Q

What is the principle of conservation of momentum?

A

If no external forces act on a system, then the total momentum before a collision is equal to the total momentum after a collision
Total momentum before = total momentum after

48
Q

Ice hockey players wear protective pads filled with foam. How do these pads help to reduce injury in the event of a collision?
(This question can appear in multiple guises by the structure of the response is always the same)

A
  • The foam increases the time taken to reduce the momentum of the hockey player to zero
  • This decreases the rate of change of momentum
  • Thus decreasing the resultant force on the hockey player, and reducing the risk of injury
  • F = Δp / Δt
49
Q

Why does a gun recoil when shot?

A

The total initial momentum of the system is zero (as nothing is moving)
Hence, when the projectile is fired the total final momentum must also equal zero
The gun recoils with an equal and opposite momentum to the projectile

50
Q

What equation links acceleration, final and initial velocity and time?

A

a = v-u / t
acceleration = (final - initial velocity) / time

51
Q

What equation links distance travelled, initial and final velocity and time?

A

Distance travelled = average velocity x time
s = 1/2 (u+v) x t

52
Q

What equation links final and initial velocity, acceleration and distance?

A

v² - u² = 2as
(final velocity)² - (initial velocity)² = 2 x acceleration x distance

53
Q

What is the thinking distance?

A

The distance travelled during a driver’s reaction time (Typically 0.5s whilst driving, free of distractions)

54
Q

What is the braking distance?

A

The distance travelled under the braking force of the car until the car stops

55
Q

What is the stopping distance?

A

The thinking distance + the braking distance

Physics GCSE (10 decks)

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