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Physics > Mechanics and Materials > Flashcards

Mechanics and Materials Flashcards

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1
Q

Scalar quantity

A

? only magnitude

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2
Q

Vector quantity

A

? Magnitude and direction

Resolve horizontally and vertically

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3
Q

Define Moment

A

? The moment of a force about a point is the product of the force and the perpendicular distance from its line of action to the point.

Moment = Fd

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4
Q

Object in equilibrium (Moment)

A

CW = CCW

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5
Q

Define couple

A

? A pair of equal and opposite parallel forces acting on the same body that do not act in the same line

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6
Q

Define Centre of Mass

A

? Where the mass of an object can be considered concentrated. The line of action that shows how gravity is acting upon the object

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7
Q

How do you find the centre of mass of an object

A

Suspending the object by a pin and then using a plum line to draw on the line of action. Switch the pin to a different position and where they cross is the center of mass.

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8
Q

Define instantaneous velocity

A

? Velocity of an object at a specific point in time.

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9
Q

Define average velocity

A

? The velocity of an object over a specified time frame. Total Displacement / Total time

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10
Q

Define uniform acceleration

A

? Where the acceleration of an object is constant

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11
Q

SUVAT Equation

A

V = u + at

s = 1/2(u+v)t

s = ut + 1/2at^2

v^2 = u^2 +2as

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12
Q

Describe the components in a projectile motion

A

The vertical and horizontal components are independent. Thus they can be evaluated separately.

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13
Q

Define Free fall

A

? An object experiences and acceleration of g

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14
Q

Define Friction

A

? A force that opposes the motion of an object. Converts KE into heat and sound

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15
Q

Define and describe terminal velocity

A

? Occurs when the frictional force acting on an object and driving forces are equal, no acceleration.

● As they leave the plane they accelerate because their weight is greater than the air
resistance.
● As the skydiver’s speed increases, the magnitude of air resistance also increases. This
continues until the force of weight and air resistance become equal, at which point terminal
velocity is reached.

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16
Q

Newton’s 1st Law

A

? An object will remain at rest or travelling at a constant velocity, until it
experiences a resultant force.

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17
Q

Newton’s 2nd Law

A

? The acceleration of an object is proportional to the resultant force
experienced by the object

F = ma

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18
Q

Newton’s 3rd law

A

Every force has an equal and opposite reaction

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19
Q

What is the relationship between air resistance and speed

A

As air resistance increases, speed increases

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20
Q

How does uniform acceleration looks like on a velocity-time graph

A

Straight line

m = acceleration 
A = displacement
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21
Q

Define lift

A

? an upward force that acts on objects traveling fluids.
it is caused
by the object creating a change in direction of fluid flow, and it acts
perpendicular to the direction of fluid flow.

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22
Q

Experimental Method to determine d ( free fall)

A

Set up the apparatus as shown in the diagram on the next slide.
Adjust the position of the lower light gate so that h is 0.500m measured using the metre ruler. If a taller stand is available, h could be set at a higher starting value.
Switch on the supply to the electromagnet, and hang the ball bearing from it.
Reset the clock or data logger to zero and switch off the electromagnet.
Read the time on the clock or data logger once the ball bearing has passed through the light gates
Take repeat readings to find the mean time, t.
Reduce h and repeat the procedure down to a value of 0.250m. Lower values than this make it difficult to obtain accurate timings.

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23
Q

Examples of scalar quantities

A

Distance, speed, mass, temperature

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24
Q

Examples of vector quantities

A

Displacement, velocity, weight, acceleration

25
Q

Define momentum

A

? Quantity of a moving body, measured as a product of its mass and velocity.

26
Q

Law of conservation of momentum

A

? The momentum of a system is constant if there are no external forces acting on the system
? Momentum and total energy are always conserved in a closed system, but KE is not.

27
Q

Explosions

A

p = 0

28
Q

Force (p)

A

Rate of change of momentum F =m(v-u)/t

29
Q

Define Impulse

A

? Change of momentum of an object when the object is acted upon by a force for an interval of time

Ft = Mv -mu

30
Q

What quantity is represented in Area under a force-time graph

A

Impulse

31
Q

Equation for momentum

A

p = mv

32
Q

Elastic collisions

A

Momentum conserved, KE unchanged, bounce off each other

33
Q

Inelastic Collisions

A

Momentum conserved, KE changed, Join together

34
Q

Application to Vehicle safety

A

Seat belts, crumple zone.

35
Q

Define work

A

? Amount of energy transferred when a force moves an object over a distance.

W =Fscos(theta)

36
Q

Define Power

A

? Rate of energy transfer

P = WD/t
P=Fv

37
Q

Equation to calculate efficiency

A

Useful output/total input

Useful power/total power

38
Q

Principle of conservation of energy

A

energy cannot be created or destroyed, but

can be transferred from one form to another.

39
Q

Define Density

A

? Measure of a substance’s mass per unit volume p=m/V

40
Q

Hooke’s Law

A

? The force applied is directly proportional to the extension of the material.
F = k (change) L

41
Q

Define Limit of proportionality

A

? the point after which Hooke’s law is no longer obeyed.

42
Q

Define elastic limit

A

? The maximum stress that a particular material can take before undergoing plastic deformation.

43
Q

Elastic Deformation

A

? A material that returns to its original shape after a tensile/compressive force has been removed

44
Q

Plastic Deformation

A

? A deformation of a body caused by an applied stress which remains after the stress is removed

45
Q

Define Tensile stress

A

? The force exerted per unit of cross-sectional area. Same unit as pressure (Pa/Nm^-3)

Stress = F/A

46
Q

Define tensile strain

A

? The extension per unit original length, no unit as it is a ratio.

Strain = change in length / original length

47
Q

Young modulus

A

The ratio of stress to the strain of a material. It is a measure of how stiff the material is.

Young modulus = tensile stress/ tensile strain

48
Q

Define Breaking stress

A

? is the value of stress at which the material will break apart, this value will depend
on the conditions of the material e.g its temperature.

49
Q

Define Brittle

A

A material that breaks without any noticeable yield/extension, glass. Little plastic effect.

50
Q

Ductile

A

? A material that can be drawn into wire under tensile stress, copper

51
Q

Malleable

A

A material that can be easily plastically deformed under compressive stress. eg: blue-tac

52
Q

Stiff

A

? Materials that require a lot of force for a small extension, or a large stress for a small strain

53
Q

Hardness

A

A material’s ability to scratch other materials. Diamond is a very hard material

54
Q

Strength

A

How much force a material can withstand before fracturing (breaking)

55
Q

Plastic

A

Easily shaped or moulded.

56
Q

Fractures

A

When the material completely breaks

57
Q

Stress-strain graph

A

m - Young modulus

Area -Strain energy per unit volume ( 1/2 * stress *strain)

58
Q

Energies in spring systems

A

Obeys the laws of conservation
The total energy at all points in an oscillationis the same
The ratio of kE and PE changes

Physics (9 decks)

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