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Mechanics Flashcards

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1
Q

Newtons 1st Law

A

A body will remain at rest or continue at uniform velocity, unless acted upon by a resultant force

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2
Q

Newtons 2nd Law

A

The acceleration experienced by a body is parallel and directly proportional to the resultant force acting upon it

F=ma

F = (mu-mv)/t

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3
Q

Newtons 3rd Law

A

When two bodies interact, they exert forces upon each other which are equal in magnitude, but opposite in direction

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4
Q

Resultant force

A

Only required for acceleration

Any body moving at a constant velocity does not have a resultant force acting

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5
Q

What is Mass

A

A measure of a body’s inertia - its resistance to a change in velocity

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6
Q

What do bodies with more mass have

A

Greater inertia

Require more force to change their velocity

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7
Q

What is Weight

A

Force of attraction that acts on a body - owing to the body having mass and being in a gravitational field

W=mg

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8
Q

What is the Centre of Mass and where does it lie

A

A single point at which the body’s mass can be thought to be concentrated

Lays where all lines of symmetry cross

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9
Q

CoM practical

A

Suspend the body from a position near its edge

Allow it to come to rest

Draw a line vertically down - using plumb line to guide

Suspend the body from another point

Allow it to come to rest - vertical line straight down

CoM lays where lines cross

When body is in rest - it’s in equilibrium - weight must act through CoM - gives rise to a zero moment

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10
Q

Free fall

A

Motion of a body through a drag producing medium without a drag producing device

Resultant force accelerating body (the weight) stays the same - accelerates uniformly - use dynamic equations

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11
Q

Forces acting when a body falls through the air on earth

Calculate resultant force

A

Weight and drag

F=ma

W-D=ma

a=(W-D)/m = mg/m - D/m

a = g - D/m

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12
Q

Free fall assumption

A

Drag can be ignored as drag force up isn’t same order of magnitude as weight force

Times it can’t be ignored:

Body’s mass is very small in relation to surface area

Body is falling at a considerable velocity

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13
Q

Free fall ignoring drag working out

A

a = (W-R) / m
a = W/m

W = mg

a = mg/m

a=g

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14
Q

Driving force acting on a body of a certain shape in a given fluid

A

Body accelerates
Velocity increases
Drag force increases
Resultant force decreases
Acceleration decreases

Eventually drag force = driving force

Zero resultant force - zero acceleration - constant maximum speed attained - Terminal speed

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15
Q

Terminal speed

A

Maximum speed attained by a body during free fall, when it’s weight is balanced by the drag force acting upon it

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16
Q

Principle of moments

A

For a system in equilibrium

Components in every plane are balanced

Sum of clockwise moments = sum of anti-clockwise moments

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17
Q

Support force

A

Acts where a body is in contact with a surface

Bodies balanced horizontally on a pivot - support force always acts upwards

Bodies in equilibrium - support force up must equal all forces acting down

Supports force acts at the pivot in a single support - has no moment

Two pivots = two support forces - moments about one pivot means you must take into account the moment of the support force from the second pivot - value of support force at each pivot is determined by where CoM lies

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18
Q

Only way to get system in rotation without translational motion

A

Apply a pair of forces about the pivot point - acting in the same plane but opposing directions

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19
Q

How to get system in rotation with translational motion

A

Single force about a pivot point - unbalanced force in horizontal plane

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20
Q

Couple

A

Pair of forces which give rise to a resultant moment but no resultant force

Moment of a couple = torque

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21
Q

Triangle of forces

A

Triangle that represents magnitudes and directions of three forces whose resultant is zero

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22
Q

Density

A

Mass per unit volume

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23
Q

Measure mass

A

Scales

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24
Q

Measure volume

A

Liquid - measuring cylinder

Regular shaped solids - sides using ruler/vernier callipers/micrometer - calculate volume

Irregular shapes solids - displacement can

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25
Q

Pressure

A

Normal force exerted per unit area

F / A

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26
Q

Pressure in a liquid

A

At any given depth below the surface of a liquid - pressure is determined by weight of the water above that must be supported

Greater depth - more weight of water - greater pressure

Same depth - greater density - greater weight of water - greater pressure

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27
Q

Pressure in a liquid at a given depth formula

A

Pressure - density x g x depth

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28
Q

Archimedes Principle

A

Upthrust exerted on a body is equal to the weight of the liquid displaced by the body

Upthrust = density x g x submerged depth x surface area

29
Q

Upthrust

A

Occurs whenever a body is immersed within a fluid

Results from the pressure difference that exists between the top and bottom of the fluid

30
Q

What is instantaneous speed

A

Speed of an object over a very short interval of time

31
Q

How to find instantaneous speed at a specific time

A

Draw a tangent at the gradient

32
Q

What is acceleration when the gradient of a velocity of a time graph is constant and positive

A

Constant Acceleration

33
Q

What is acceleration when the gradient of a velocity of a time graph is constant and negative

A

Constant deceleration

34
Q

What is acceleration when the gradient of a velocity of a time graph is zero

A

Zero acceleration

35
Q

What is acceleration when the gradient of a velocity of a time graph is a curve

A

Acceleration is changing

36
Q

What is the area under a velocity-time graph

A

Displacement

37
Q

What is the area under a velocity-time graph

A

Displacement

38
Q

What is thinking distance

A

Distance travelled between the moment when you first see a reason to stop, to the moment when you use the brake

39
Q

What is braking distance

A

The distance travelled from the time the brake is applied until the vehicle stops

40
Q

What is stopping distance

A

Total distance travelled from when the driver first sees a reason to stop, to when the vehicle stops

41
Q

Thinking distance formula

A

Speed x reaction time

42
Q

When is an object said to be in free fall

A

When an object is accelerating under gravity, with no other force acting on it

43
Q

What is the value for free fall

A

g

44
Q

Equation for force parallel to the slope

A

W x sin theta

mg x sin theta

45
Q

Equation for force perpendicular to the slope

A

W x cos theta
mg x cos theta

46
Q

What is normal contact force equal to

A

mg x cos theta

47
Q

Define Drag

A

A frictional force that opposes the motion of the object

48
Q

What affects drag

A

Speed
Shape
Roughness
Texture

49
Q

What is pressure at the base equal to

A

Weight of the column divided by A

50
Q

What is pressure directly proportional to

A

height

51
Q

What does pressure not depend on

A

Cross sectional area

52
Q

Upthrust at the top surface of an object

A

height x density x gravity x area

h is the submerged depth

53
Q

Force at the bottom surface of an object

A

(h + x) x density x gravity x Area

x is height of object

h is the submerged depth

54
Q

When will an object sink

A

If upthrust is less than the weight of the object

55
Q

When will an object float

A

upthrust = weight

56
Q

What is momentum

A

Mass x velocity

57
Q

What is the principle of conservation of momentum

A

For a system of interacting objects, the total momentum in a specified direction remains constant, as long as no external forces act on the system

58
Q

Describe perfectly elastic collisions

A

Momentum is conserved
Total energy is conserved
Total kinetic energy is conserved

59
Q

Describe inelastic collisions

A

Momentum is conserved
Total energy is conserved
Total kinetic energy is conserved

60
Q

What is net force directly proportional to

A

Rate of change of momentum

Newtons second law

61
Q

Newtons second law

A

F = (k (constant) x change in momentum) / change in time

62
Q

When do we use F=ma

A

When the mass of the object remains constant during the period of acceleration

63
Q

What happens to momentum because of Newtons 3rd Law

A

Net change is 0 therefore it always conserved

64
Q

What is the impulse of a force

A

The change in momentum

65
Q

Impulse equation

A

F x change in time = change in momentum

66
Q

What is the area under a force time graph

A

Impulse

67
Q

Resolving momentum in the horizontal plane

A

total initial momentum = total final momentum

m1v0 = m1v1cos(theta) = m2v2cos(theta)

68
Q

Resolving momentum in the vertical plane

A

total initial momentum = total final momentum

m1v0 = m1v1sin (theta) = m2v2sin(theta)

Physics (19 decks)

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