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Mechanics Level 1 > Mechanics > Flashcards

Mechanics Flashcards

0
Q

Go to page 160 for graph description

A

NOW

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1
Q

Formula for speed?

A

d/t

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2
Q

If I did 2 hours of driving at 100km/h then had lunch for 1 hour and then did 2 hours of driving at 90km/h again and reached Taupo, what’s my average speed? and how long was the journey?

A 
First bit: 2 X 100 = 200km travelled
Second bit: 2 X 90 = 180km travelled
Total travelled: 200 + 180 = 380km
Total hours: 2 + 1 + 2 = 5hours
Average speed: 380/5 = 76km/h
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3
Q

If the d t graph is like:
/
__/

but curved, meaning?

A

it’s accelerating

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4
Q

D T graph like:
__
/
/

A

Decelerating

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5
Q

If dt graph like:

   /
 /
/
A

Constant speed

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6
Q

Define acceleration

A

The rate at which the velocity of an object is changing is known as acceleration

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7
Q

What is negative acceleration also known as?

A

Deceleration

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8
Q

Formula for acceleration

A

at = v - u
or v = u + at
where u = initial speed
and v = final speed

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9
Q

Fancy equation for d

d =

A

d = ut + 1/2at^2

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10
Q

Fancy equation for v^2

v^2 =

A

v^2 = u^2 + 2ad

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11
Q

If on a v t graph, a linear line, meaning?

A

Acceleration

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12
Q

If linear line going down on a v t graph, meaning?

A

Deceleration

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13
Q

On a v t graph, if straight line, meaning?

A

Constant speed

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14
Q

If no line on v t graph, meaning?

A

Stationary

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15
Q

What is the gradient of v t graph?

A

acceleration

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16
Q

What is gradient of d t graph?

A

Velocity

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17
Q

Define velocity and what is the difference between velocity and speed?

A

Speed plus direction gives the velocity of an object
Speed in a given direction
eg: 50km/h East

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18
Q

What is speed? When is something said to have speed?

A

Speed is how far something travels in a certain time.

Anything which has motion (i.e. is moving) is said to have speed.

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19
Q

If a vehicle is at constant speed then……….?

A

It is covering equal distances in equal times.

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20
Q

What does the area under the v t graph give? Why?

A

Distance travelled because v X t = d

21
Q

Define forces. What do all forces have?

A

Forces are a push, pull or twist that can change the speed, direction or shape of an object. They have a size (Newtons) and a direction.

22
Q

Difference between contact and non-contact forces, also give eamples.

A

A contact force is one where the forces is applied through direct contact with an object.

A force field acts on an object over a distance and there is no direct “touching”. Also, the strength of the force field decreases as the object moves away.

Contact: push, friction, support, thrust, drag…
Non contact: magnetic, electrostatic, gravitational force (weight)

23
Q

What is net force?

A

The combination of forces that act on an object is called net force.
Forces in same direction add and opposite directions subtrace.

24
Q

What is a balanced force?

A

Balanced forces (Fnet = 0N) are equal and opposite. No acceleration.
Stationary object remains stationary
Moving object moves with same speed & direction.

25
Q

What are unbalanced forces?

A

Fnet =\ 0N
Object accelerates
Stationary object begins to move
Moving object will change speed and/or direction

26
Q

Newton’s first law of motion is called……? and What does it state?

A

Law of inertia
A body remains at rest or moves in a straight line at a constant speed unless acted upon by a force

An object at rest will stay at rest
An object in motion will stay in motion
Unless acted upon by a force.

27
Q

What does Newton’s second law state?

A

The acceleration (a) of an object is directly proportional to the amount of force (f) applied to that object. It is inversely proportional to the mass (m) of that object.

F = ma

Size of the acceleration depends on the net force and mass of the object.

28
Q

Define mass. What are its units?

A

Mass is the amount of material of an object.

Units: kg or g

29
Q

Define weight. What are its units? Formula?

A

Weight is the force with which the object pushes down on what it is resting on. The downward pull of gravity.
Units: Newtons
W = mg

30
Q

Difference between weight and mass?

A

Mass stays the same no matter where the object is but weight changes in different gravitational fields

31
Q

What is friction?

A

The force that opposes the motion of an object.

Reaction forces created when two surfaces slide past eachother, in the direction opposite the object motion.

32
Q

When is friction helpful, problematic and how can it be reduced?

A

Bike tires grip road, parachutes work with friction.

Air resistance slows vehicles down, wears machinery out.

Lubrication with oil, wheels or ball-bearings, streamlined shapes to reduce air resistance.

33
Q

What is static friction?

A

Force that stops objects moving when they are pulled.

34
Q

Air resistance & terminal velocity para.

A dropped object initially falls downwards f………

A

faster and faster (acc due to gravity, 10m/s/s) and net force is downward.
On earth, air resistance increases as object moves faster, so net downward force gets smaller
Eventually, gravity force is balanced by air resistance and net force = 0N
Object continues to fall at speed when forces balanced, called TERMINAL VELOCITY.

When objects fall freely through the air from a large height, they don’t continue to accelerate but eventually reach a constant speed. This is b/c air resistance increases as speed increases and eventually balances the downward force of gravity so there’s no further acceleration -> TERMINAL VELOCITY

35
Q

What is pressure?

A

Force per unit of area acting on a surface.
Pressure is inversely related to the area of contact
eg -same force over SMALLER AREA, MORE PRESSURE on surface.
-same force over LARGER AREA, LESS PRESSURE on surface.

36
Q

Pressure from gases and liquids…….

A

……is experienced in all directions as freely moving molecules bombard all surfaces

37
Q

What is air pressure and what is water pressure?

A

Air pressure: pressure exerted by weight of air on object
-reduces with altitude
Water pressure: pressure exerted by weight of water on object
-increases with depth.

38
Q

Does water have more pressure than air?

A

Yup, more water than air in same space

39
Q

Formula for pressure?

A

P = force/area

Pressure created by a force acting on an area is given by this formula

40
Q

What is energy defined as?

A

The capacity to do work (i.e. the capacity to exert a force that will cause motion - makes things happen)
unit: Joules
Energy takes many forms and changes readily from one form to another.

41
Q

GPE is….

A

….the potential energy an object has because of height.

Ep = mg/\h

Ep is directly proportional to h

42
Q

What’s kinetic energy?

A

The energy an object has because it is moving

Ek = 1/2mv^2

43
Q

How is Ek related to m and v^2?

A

Directly proportional to mass
-double mass, double Ek
Related to SQUARE OF SPEED
-double speed, four times Ek

44
Q

What is the law of conservation of energy? (2)

A

Energy cannot be created or destryped; it is only transformed from one form to another.
In energy conservations, some energy is often transformed into heat or sound by friction
Ep lost = Ek if no friction
Ep lost =\ Ek the missing energy is lost as friction

45
Q

What is work done? (2)

A

Work done is energy transformed when a force moves an object
no movement = no work
Energy is transferred as kinetic energy and/or GPE
sometimes, energy is lost as heat due to friction

46
Q

“Less force required means it’s easier”

Explain further

A

Lifting objects straight up requires more force over shorter distance
small d, large f
Pushing objects up a ramp requires less force over a longer distance
large d, small f

47
Q

Formula for work done?

A

W = fd

48
Q

Formula for Power?

A

P = w/t

49
Q

What’s power? Powerful machines can do……….

A

Power is how fast energy is changed or how fast work is done

Mechanics Level 1 (1 decks)

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