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Physics > Mechanics > Flashcards

Mechanics Flashcards

1
Q

Moment definition

A

The force multiplied by the perpendicular distance from the pivot to the line of action of the force

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2
Q

Unit of moment

A

Nm

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3
Q

Principle of moments

A

If a system is in equilibrium, the sum of the clockwise moments about any point equals the sum of the anticlockwise moments about the same point

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4
Q

Moment equation

A

M=Fd

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5
Q

What’s a couple

A

A pair of forced of equal size which act parallel to eachother but in different directions. Coplaner forces

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6
Q

How to calculate moment of a couple

A

Size of on of the forces x perpendicular distance between lines of action

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7
Q

Centre of mass definition

A

The single point an objects whole weight acts through

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8
Q

Find centre of mass

A

-Cut piece of card into irregular shape
-Hang card with string freely from a point
-Use ruler to mark a line where the string is
-Hang from a different point repeat 3x
-Centre is where lines intersect

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9
Q

Centre of mass: When will an object be stable?

A

Low centre of mass + wide base area

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10
Q

Centre of mass: When will an object topple over?

A

If a vertical line drawn downwards from centre of mass falls outside base area

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11
Q

What does the gradient of a displacement time graph represent

A

Velocity

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12
Q

What does a curved line show on a displacement time graph

A

Change in velocity
Acceleration

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13
Q

What does the gradient of a velocity time graph represent?

A

Acceleration

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14
Q

How to find displacement on a velocity time graph

A

Area under graph.
Area above x= positive change
Area below x= Negative change(returning to starting point)

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15
Q

What’s does a curved line show on a velocity time graph

A

Increasing /decreasing acceleration

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16
Q

Area under line on acceleration time graph

A

The change in velocity

17
Q

Newton’s 1st law

A

If there are no resultant forces acting on an object it will either stay at rest or travel at constant speed in a straight line

18
Q

Newton’s 2nd law

A

The acceleration of an object is proportional to the resultant force acting on it

19
Q

Newton’s 3rd law

A

If object A exerts a force of object B, then object B exerts an equal but opposite force on object A

20
Q

When is an object in freefall

A

When the only force acting on it is its weight

21
Q

Galileo experiment

A

-Rolled balls with similar masses down a slope
-Acceleration still caused by gravity but rolled slower: easy for timing /air resistance negligible.
-He timed how long it took for the balls to roll down different lengths - Found distance travelled was always the same
-Proved acceleration was uniform regardless of mass

22
Q

Projectile definition

A

An object where the only force acting on it is its weight.

23
Q

What to use to calculate vertical components

A

Suvat equations

24
Q

Effects of air resistance on projectiles

A

-Horizontal velocity will slowly decrease to 0 as horizontal force is now acting
-It will therefore not travel as horizontally
-Projectile will gain vertical speed more slowly

25
Q

How to calculate horizontal component

A

D=ST

26
Q

Friction definition

A

A force that opposes motion, turns kinetic into thermal energy, can never speed things up or start them moving

27
Q

Drag definition

A

Friction caused by a gas or liquid

28
Q

How does a wing generate lift

A

1) It diverts air down changing direction of the air by forcing it down
2)Newtons 3rd law air exerts equal and opposite force up on wing
3) Bernoulli’s principle

29
Q

What does drag increase with

A

-Surface area
-Speed
-Density

30
Q

How does an object reach terminal velocity moving down through fluid

A

-Initially accelerates
-As velocity increases drag increases
-Weight and drag forced will balance out

31
Q

What is terminal velocity

A

When frictional forces are equal to driving forces acting on an object making resultant force 0. Object moves in constant velocity

32
Q

principle of conservation of momentum

A

The total momentum before a collision is equal to the total momentum after the collision provided no external forces act

m1u1+m2u2=m1v1+m2v2

Physics (7 decks)

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