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AS Level CIE physics > Dynamics > Flashcards

Dynamics Flashcards

1
Q

What is dynamics?

A

Dynamics is the study of motion and the force causing the motion.

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2
Q

What is a force?

A

Force is a push or pull of one object on another.

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3
Q

What are the two categories of force?

A

Applied force and Net/Resultant force and resistive force.

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4
Q

What are the two types of applied forces?

A

Friction and Drag force.

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5
Q

What are the two types of drag forces?

A

Air resistance and Fluid Drag.

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6
Q

What are the types of resultant/net force?

A

Weight
Tension
Upthrust
Normal Reaction force
Centripetal force

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7
Q

What is an applied force?

A

a force exerted by an external source is called an applied force.

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8
Q

Give examples of applied force.

A

Force of a horse on a cart
Force of Friction between a road and tire on a car.

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9
Q

What is a resistive force?

A

Resistive forces are forces that always oppose motion.

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10
Q

Define Friction.

A

A stopping force between two sliding surfaces due to interlock between surfaces is called friction.

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11
Q

What are the factors which affect friction?

A

Nature of surfaces
Normal reaction/Contact Force

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12
Q

What are some benefits of friction?

A

Friction is beneficial when we need to stop a car or bike etc.
Friction is important when tying a knot.
Friction between the road and the tire and a shoe and the track to help you move.

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13
Q

What are some disadvantages of friction?

A

We need to spend fuel to overcome friction.
Friction generates unwanted heat.
Friction causes wear and tear in mechanical parts.

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14
Q

Define Tension.

A

tension is a pulling force exerted by a rod, chain or rope.

Tension acts along the rope away from both ends.

In one rope there can only be one tension.

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15
Q

Define Weight.

A

Weight is the gravitational force of nearby mass. (usually nearest celestial mass)

Weight=mass x gravitational field strength.

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16
Q

What can force do?

A

●Force can change motion, accelerate, decelerate or change direction of motion.
●Force can generate heat (Friction)
●Force can turn an object, produce moment or turning affect.
●Force can deform an object. (check notes)
●Force can cause pressure.

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17
Q

Define drag force.

A

When a solid moves in a fluid, it exerts force on molecules of fluid. The molecules of fluid exert an equal but opposite force on the solid object as a reaction. This reaction force is called drag force.

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18
Q

What is the name of drag force to due to air?

A

Drag force due to air is known as air resistance.

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19
Q

What does drag force depend upon?

A

Drag force depends upon:
Velocity/Speed of motion=D∝v^2
Area of front of the object=D∝A or D∝d^2 (where d is the diameter square)
The density of the medium D∝ρ

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20
Q

What are two types of ways materials can behave when deformed?

A

When deformed materials behave differently.

The two categories are:
Elastic Materials
Plastic Materials.

21
Q

What are elastic materials.

A

Elastic materials are those which gain back their original size and shape when deformed.

22
Q

What are Plastic materials.

A

Plastic materials are those materials which get permanently deformed and don’t gain back their original shape and size.

23
Q

Define elasticity.

A

Elasticity is the ability of an object to regain its original shape and size when the deforming force is removed.

24
Q

Define plasticity.

A

Plasticity is the ability of a material to gain a new shape and deform permanently even when the deforming force is removed.

25
Q

Define the elastic limit.

A

Materials that are elastic are not elastic forever. If an elastic material is deformed beyond a certain value it gets permanently deformed. Such a value is called the elastic limit.

Elastic Limit can be a limit of load or a limit of extension.

26
Q

What is the formula for extension.

A

Extension=stretched length-unstretched length.

ΔL=l-l0
Δ=x=e

27
Q

State Hooke’s Law.

A

Hooke’s law states that extension is directly proportional to deforming force within elastic limit.

extension∝deforming force
or
restoring force∝extension
deforming force=restoring force
(when elastic limit is not reached)

28
Q

Defining deforming force.

A

Deforming force is the force used to produce deformation.

29
Q

Define restoring force.

A

Restoring force is the force that the deformed object exerts to gain back its original shape and size.

30
Q

State the law of conservation of energy?

A

The law of conservation of energy states that energy cannot be created nor destroyed. Energy is always conserved.

31
Q

What does the gradient in a force by extension graph within elastic limit represent?

A

The gradient can either represent Loading (upwards direction) or unloading (downward direction).

32
Q

What does the area under a loading force/extension graph represent under elastic limit?

A

Stored strain energy or work done on spring.

33
Q

What does the area under an unloading force/extension graph represent under elastic limit..

A

Work done by spring.

34
Q

Describe the relation between an unstretched string and work or energy.

A

When a spring is unstretched no work or energy is needed.

35
Q

Describe the relationship between an increasingly stretched spring.

A

Work is done on the system (spring), so strain energy is increasing.

36
Q

Describe the relationship between a spring which has been stretched to its maximum and then let go.

A

Maximum strain energy

37
Q

Describe the relationship between an spring which moves back towards its unstretched condition/position.

A

Work is done by the spring, elastic potential energy decreases. Kinetic energy and/or other forces of energy increase.

38
Q

What are the different points which can be reached in a force by extension graph.

A
  1. Limit of proportionality.
  2. Limit of elasticity.
  3. Yield Point
  4. Breaking point
39
Q

Describe what is indicated by the limit of proportionality in a force by extension graph.

A

Hooke’s law is only obeyed before point P.
After point P is passed the graph is no longer a straight line.

40
Q

Describe what is indicated by the limit of elasticity in a force by extension graph.

A

Object is only elastic before point E. At or beyond point E the object develops permanent changes.

If an object is let go after P but before E it will go back to its original unstretched size and shape.

But if an object is stretched beyond E, it will come back but not to its original and size, it will have some permanent changes in size.

41
Q

Describe what is indicated by the yield point in a force by extension graph?

A

If an object is stretched to the yield point or beyond the yield point it will not come back at all so this point is the yield point.

42
Q

Describe what is indicated by the breaking point in a force by extension graph?

A

At the breaking point the objects structural integrity is compromised and it breaks at the weakest point.

The weakest point is the least effective cross sectional area.

43
Q

What are the different properties of materials?

A

The different properties of material include:
Malleable,
Ductile,
Brittle,
Polymers (amorphous).

44
Q

What are brittle materials?

A

Materials that don’t change shape but break. For example: glass, cast iron etc

45
Q

Where are brittle materials used?

A

Brittle materials break but do not get permanently deformed. This is why these materials are used in machinery specifically in engine and alloy rims.

46
Q

What is the relationship between hooke’s law and polymer (amorphous) materials.

A

Polymers never show any obedience to Hooke’s Law. Force and extension are not directly proportional but there is a positive correlation.

47
Q

What is the formula for stress?

A

Stress= Deforming force/Cross sectional area.

σ=F/A

Nm-2 or Pascals= Newtons/Meter Square

48
Q

What is the formula for Hooke’s law?

A

since f∝e
F=Ke

Where K is spring constant and used as constant of proportionality.

k=f/e constant=f/e

Where K has Nm-1 units.

AS Level CIE physics (8 decks)

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