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Physics Ocr A Level > 3. Forces And Motion > Flashcards

3. Forces And Motion Flashcards

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1
Q

Define speed, the equation used to calculate speed and the si units

A

The rate of change of distance
Speed =distance/time
ms^-1

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2
Q

Define displacement

A

The distance an object has traveled in a given direction, vector with both magnitude direction

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3
Q

Define velocity, the equations used to calculate velocity and the SI units

A

The rate of change of displacement, or speed in a given direction.
Velocity= change in displacement/ time
Ms-1

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4
Q

Define acceleration, the equation used for acceleration, and the SI units

A

The rate of change of velocity,
Acceleration=change in velocity/time
Ms^-2

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5
Q

What does a straight, horizontal line on a displacement time graph represent

A

Stationary object

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6
Q

What does a line with a constant gradient represent in a displacement-time graph

A

Constant velocity

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7
Q

What does a curved line represent on a displacement-time graph?

A

Acceleration or deceleration

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8
Q

What does a straight horizontal line represent on a velocity-time graph?

A

An object moving with constant velocity

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9
Q

What does a line with a constant, non-zero gradient represent on a velocity-time graph?

A

An object that is accelerating or decelerating

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10
Q

What does the area under a velocity-time graph represent

A

Displacement

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11
Q

What does the area under an acceleration-time graph represent

A

Velocity

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12
Q

Describe how the terminal velocity of an object can be determined using light gates

A
  • set up the light gates vertically and measure the distance between them
  • connect them to a data logger and then release an object from rest above them, measuring the time it takes for the object to travel between the two gates
  • using the time and the known distance, you can calculate the velocity using v=d/t
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13
Q

Describe how light gates can also be used to investigate conservation of momentum

A
  • place two carts on a linear air track with repelling magnets so that they do not stick together.
  • Attach card to the top of each cart so that they break the beams of the light gates when they pass.
    -keep one cart stationary and push the other towards it, measuring its velocity before the collision.
  • then measure the velocity of both carts after the collision and calculate the momentum before and after
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14
Q

Define g

A

The acceleration of free fall,the acceleration of an object in response to the gravitational attraction between the earth and the object

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15
Q

Describe the experiment to determine ‘g’ using an electromagnet

A
  • An electromagnet holds a steel ball suspended a measured distance above a surface, then start the timer when the electromagnet is deactivated, and stop it when the surface is hit
  • As the ball was initially resting, u=0
  • the distance and time are known, so use a SUVAT equation : s=ut+1/2at^2
    -a is g, 9.81
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16
Q

How does the horizontal velocity of a projected ball change from its laugh until it hits the ground?

A

The horizontal velocity remains the same as there is no acceleration in the horizontal direction

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17
Q

In projectiles motion, what is the vertical acceleration?

A

The vertical acceleration is equally to g downwards

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18
Q

Describe what happens when a resultant force F acts on a body with mass m

A

The body will accelerate in the direction of the resultant force. The resultant force is related to mass and acceleration by the formula:
F=ma

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19
Q

Give 3 examples of common forces and explain briefly what they do

A
  • weight- the gravitational force acting on an object, through its centre of mass
  • Friction - the force that arises when two surfaces rub against each other
  • drag - the resistive force on an object travelling through a fluid
  • tension - the force within a stretched cable or rope
  • upthrust -the upward buoyancy force acting on an object when it is in a fluid
  • Normal contact force- the force arising when an object rests against another object. It acts perpendicular to the plane of contact
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20
Q

What is meant by drag

A

The frictional force that opposes motion through a fluid.

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21
Q

What is meant by terminal velocity

A

When the forces acting on the falling object are balanced so the resultant force is 0. The acceleration is therefore zero

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22
Q

What is the principle of moments

A

For an object in equilibrium, the sum of the clockwise moments is equal to the sum of the anticlockwise moments

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23
Q

What is a moment

A

A turning force
=Force x perpendicular distance to pivot

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24
Q

What is meant by a couple

A

A pair of equal and opposite coplanar forces that have equal magnitude and opposite direction,applied to a body parallel to each other but not along the same line

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25
Q

If you have a uniform object, where would its centre of mass be ?

A

At the geometric centre of the object

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26
Q

Describe what is meant by density

A

Mass per unit volume of a substance. The unit is kg m^-3

27
Q

Describe what is meant by pressure

A

The normal force excerted on a surface per unit area.

28
Q

What is the force that an object submerged in a fluid experiences

A

Upwards force - up thrust
Due to the pressure at the bottom surface of the object being greater than at the top

29
Q

State Archimedes principle

A

The upthrust exerted on a body immersed in fluid, whether partially or fully submerged, is equal to the weight of the fluid that the body displaces when the object floats. An object will sink if the upthrust is smaller than the weight

30
Q

Define work done

A

The product of the magnitude of the force and the distance moved by the object in the side of the force. Joules (J)

31
Q

Define kinetic energy and give its SI units

A

The energy associated with the motion of an object with mass. The SI base unit is kg m^2 s^-2

32
Q

Define gravitational potential energy

A

The energy of an object due to its position in a gravitational field

33
Q

Define elastic potential energy

A

The energy stored by an object as a result of a reversible change in its shape

34
Q

State the principle of conservation of energy

A

In a closed system, energy cannot be created or destroyed but only transferred from one form to another

35
Q

In a closed system where an object is moving up and down, derive a formula for the velocity of an object in a gravitational field.

A

All initial GPE is converted to KE as the object falls, and this KE is converted back to GPE as it rises.
mgh=1/2mv^2
So v= √2gh

Since there is no ‘m’, mass has no effect on the final speed - the acceleration of free fall is the same for all objects

36
Q

The rate of work done is equal to…

A

Power

37
Q

What is meant by extension and compression of a string ?

A

Tensile forces act away from the centre of the spring in both directions and will stretch it out causing the spring to extend
Forces acting towards the centre of the spring in both direction is called compression

38
Q

What happens to the spring when tensile/compressive forces are exerted

A

The spring undergoes ‘tensile deformation’ or ‘compressive deformation’

39
Q

What is Hooke’s law

A

In a material showing Hooke’s law, the force applied is directly proportional to the extension in length, up to the elastic limit
Force = spring constant x change in length

40
Q

What is meant by tensile stress ?

A

Force per unit area

41
Q

What is tensile strain

A

Extension over original length

42
Q

What is the difference between elastics and plastic deformation?

A

Elastic deformation- when the force is removed the object will return to its original shape

Plastic deformation- the object will not return to its original shape after the force is removed

43
Q

How is energy stored during elastic deformation

A

The work down is transferred and stored as elastic potential energy

44
Q

Describe the energy changes that occur during plastic deformation

A

The material is stretched and the energy from the work done is used to break the bonds between the molecules, causing permanent deformation

45
Q

What is breaking stress

A

The amount of stress a material can take without breaking

46
Q

What is meant when a material is describe as brittle

A

It does not extend much when a force is applied, and breaks rather than stretch under force

47
Q

What is elastics limit

A

The point after which plastic deformation occurs.

48
Q

What does the area under a force extension graph represent

A

The energy stored in the material

49
Q

What’s the equation to calculate elastics strain energy in terms of spring constant and extension

A

E= 1/2 k x^2

50
Q

What is Young’s modulus

A

Tensile stress / tensile strain

51
Q

How do you find the round Young’s modulus from a stress-strain graph

A

The gradient

52
Q

If an object is in equilibrium it mean the object is …

A

Not accelerating either stationary or moving at a constant velocity

53
Q

Which of newtons laws state ‘every action has an equal and opposite reaction force’

A

Newtons 3rd law

54
Q

What is Newton’s second law

A

F=ma
The resultant force of an object is proportional to the rate of change of momentum of the object and in the same direction

55
Q

What is Newton’s first law

A

An object at rest or moving with constant velocity will stay that way unless a resultant force acts upon it

56
Q

What is the difference between elastic and inelastic collisions

A

In an elastic collision the KE before is equal to the KE afterwards,
In inelastic collisions the KE at the end is not equal to the KE at the start - energy is lost to surroundings

57
Q

Give an equation to calculate momentum

A

Mass x velocity

58
Q

True or false - linear momentum is only conserved in elastic collisions

A

False - linear momentum is always conserved

59
Q

The rate of change of momentum can also be described as …

A

Resultant force

60
Q

What is impulse

A

The change in momentum or
the rate of change of the resultant force

61
Q

What does the area under a force-time graph represent

A

Impulse

62
Q

What is mean by the principle of conservation of energy

A

Energy cannot be created or destroyed, only transferred into other forms of energy
Therefore the total energy in a closed system would always remain the same

63
Q

What is the equation used for the principle of conservation of momentum in one-dimensional collisions

A

m1u1+m2u2=m1v1+m2v2

Physics Ocr A Level (4 decks)

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