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Physics > Seesaws > Flashcards

Seesaws Flashcards

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0
Q

2 Physical Quantities of Rotational Motion?

A

1) Angular Position (Rotation)
2) Angular Velocity

Vector quantities

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1
Q

Newtons First Law Rotational Motion

A

A rigid object that’s not wobbling & free of external torques, rotates at constant angular velocity.

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2
Q

i) Rotation to your right

ii) Rotation to your left

A

i) Downward rotation

ii) Upward rotation

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3
Q

3 ways measure Angular Position

A

1) As a degree ex. 90*
2) Rotationally ex. quarter, half turn
3) Radius ex. Pi/ 2 radius down

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4
Q

Angular Velocity def & tells (3)?

A

Rate objects angular position change w/ time

Tells:

1) speed object going through angles
2) axis object’s spinning
3) (right hand rule) specific direction about axis

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5
Q

Torque

A

Twisting force causing rotation.

-changes pivoting objects angular velocity & violates N’s 1st Law of Rotational Motion (has external torque/influence & .•. not rotate constant angular velocity)

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6
Q

Seesaws Rotational Inertia affected every time_____?

A

Seesaws ends hit ground (exerting external torque)

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9
Q

Angular Acceleration

A

Rate at which angular velocity change w/ time

- vector quantity of rotational motion

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10
Q

Net Torque

A

1/more total torques acting upon object

- causes angular acceleration

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11
Q

Angular Acceleration causes (2)?

A
  1. Net Torque

2. Rotational Inertia (mass): resistance to angular acceleration

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12
Q

A larger net torque has a ____ acceleration & a smaller net torque has a _____ acceleration

A
  1. Larger

2. Smaller

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13
Q

Angular Acceleration proportional (keeps constant ratio)?

A

Net Torque acting upon object

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14
Q

Angular Acceleration inversely proportional?

A

Seesaws rotational mass

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15
Q

Newton’s 2nd Law of Rotational Motion

A

Angular Acceleration = net torque/ rotational mass

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16
Q

Torques produce x & x produces Torques

A

Forces

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17
Q

Can’t produce torque in what direction from objects centre of rotation?

A

Toward/away from/ on objects’ centre of rotation

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18
Q

Can produce torque in what direction from objects center of rotation?

A

Exerting force perpendicular to lever arms vector (amount & direction: determine 1 point in space relative another) direction.

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19
Q

Objects vector extends from?

A

Objects centre of rotation to point where force exerted (extension b/w points is vector)

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20
Q

Torque =?

A

Lever arm • force (only force perpendicular to lever arm incl.)

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21
Q

Torque you exert on bolt (w/wrench) about its centre of rotation=?

A

Your force• (wrenches) lever arm extension

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22
Q

Lever

A

A rigid bar resting on a pivot.

23
Q

Forces are at ____ to lever arms

A

Right angles

24
Q

Torques are located?

A

90• horizontal to the downward force & perpendicular to the lever arm.

25
Q

2 ways seesaw balanced?

A

1) sum of torques = 0 (cancel out)

2) riders & seesaw together have Center of Gravity vertically above pivot & .•. produce no torque.

26
Q

The two torques produced by the objects on the seesaw are____ each other.

A

Opposite.

27
Q

Moving object (& force) position lower down lever arm (closer to pivot) increases/decreases torque it produces.

A

A shorter lever arm decreases the torque it produces & is closer to the COR.

28
Q

To produce 0 torques (balance) objects w/ same weight, must be equidistant from ____ & .•. have same _______.

A

The center of rotation & .•. have same lever arm distances from pivot.

29
Q

The lever arms are in the same direction so the objects____ are in the same direction.

A

Torques

30
Q

Center of Gravity

A

The effective location of an objects weight (downward acceleration)

  • all about forces (gravity)
  • point over which object can be perfectly balanced; net torque due to gravity about that point = zero
31
Q

Center of Mass

A

Effective location objects mass, it’s natural pivot

  • all about inertia & motion
  • the average location of the mass distribution
  • objects Center of rotation: Point about which all physical quantities of rotational motion are defined.
  • point that stays put as object spins (the pivot)
32
Q

For (small) objects…..

A

G

33
Q

COG proportional ____

A

Centre of mass

35
Q

Riders @ ends of board higher/lower rotational mass?

A

Higher & .•. riders closer to pivot have lower rotational mass.

36
Q

Every piece of____ contributes to an objects rotational mass & depends on (2)?

A

Mass:

1) where portion ordinary mass is
2) how far portion ordinary mass from pivot (axis of rotation)

37
Q

Rotational mass contributed by ordinary mass=?

A

Ordinary mass • distance b/w ordinary mass & axis of rotation

38
Q

Rotational Mass depends on____?

A

The location of your axis of rotation

39
Q

Tennis Racket has 3 rotational masses (ordered by rotation)

A

Smallest: rotation about the vertical axis (most of mass close to axis)

Larger: rotation about the horizontal
axis.

Largest: when COR located at either end of racket & pivot about such point.

40
Q

Two objects dropped simultaneously w/ same force & at same distance from ground but different masses, which falls first?

A

Object w/ more angular acceleration & .•. more angular velocity. Object w/ < mass.

41
Q

You fall of a cliff, what’s the cause (i) & resistance (ii) angular acceleration of your body?

A

(i) C: Net Torque on you (due to gravity)

(ii) R: Your rotational mass

42
Q

Rotational Mass=?

A

Mass• distance^2

43
Q

You & child 1/2 your height fall @ same angle, same distance swimming pool

Who hits water 1st?

A

The child has more angular acceleration & more angular velocity.

  • You have 2x weight • 2x lever arm (2x as far your COG from axis of rotation- feet) = 4x Net torque
  • You have 2x mass • 2x distance (on average) from AxofRot
    RotMass= mass• distance^2
    .•. 2x mass • 2x distance^2 =
    8x rotational mass of child.

Have 4x net torque but 8x rotational mass.
Angular Acceleration = Net torque/mass
4/8=
1/2 Angular Acceleration vs child.

48
Q

Unsupported object thrown straight up in air doing 2 types motion?

A

1) Translational- it’s center of mass falling in arc of falling objects
2) Rotational- rotating about its center of mass (it’s natural pivot)

49
Q

Find objects center of mass method?

A

Place object on flat surface & spin it: object naturally spins about its center of mass (point stays put as object spins)

75
Q

The farther riders mass from the pivot

the greater seesaw’s _____ _______ ____ & the slower it’s _____ _______.

A

1) overall rotational mass

2) angular acceleration

86
Q

How do seesaw riders riders affect each other?

A

They support each other (cancel weights- keep from falling) & exchange energy (through seesaw & torques) as seesaw rotates back & forth

  • 1 exerts torque on 2 about the pivot
  • 2 exerts torque on 1 about the pivot
87
Q

N’s 3rd Law of Rotation

A

For every torque object (i) exerts on (ii), object (ii) exerts an equal but oppositely directed torque on object (i).

88
Q

Torque Units

A

S.I: Nmeter (m away from pivot)

Eng: FootPound (1 pound/foot away from pivot)

89
Q

When lowering (unbalancing) seesaw lowered & raised object transfer energy, what occurs w/ distance

A

Work= force•distance

  • Lowered object has > (downward) force but < distance
  • Raised object has < (upward) force but > distance
  • Both work cancel each other out & obey N’s 3rd law rotation
90
Q

To increase work on screwed nail with hammer (plucker)…

A

Increase the lever arm distance from pivot.

Work You’re doing on hammer:
Small force & large distance.

Work hammer doing on nail:
Large force & small distance

94
Q

When the gravitational field across an object is uniform _____ & ______are identical.

A

COG & COM

Physics (5 decks)

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