Flashcards in KRSE3LEC18 Deck (27):

1

## Angular kinetics of “uniform angular motion”

###
- Any force which causes a body to deviate from its straight-line path is called a “radial force”, (Fr)

- Acts perpendicular to the linear path.

2

## "centripetal” force

### For a body in curvilinear motion, the force keeping the body in the curved path

3

##
Can you give an example of a centripetal force?

### Tying a string to a piece of metal and twirling it around.

4

##
The string maintains a centripetal force.

If the string is cut

### the path the metal flys off at is tangential to the radius of the circle

5

##
What is the force acting on the piece of metal once the tension in the string is released?

### centrifugal

6

##
What about “centrifugal” force?

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Force that is going away from it, while centripetal is force going towards center

7

## Radial Acceleration

###
The object moving around the curve will have the same velocities but because they are changing direction they will have varying accelerations.

These accelerations are directed towards the center - ar

8

## Radial Acceleration equation

###
ar = V^2/r

Where V is the velocity of the body & “r” the radius of the circle.

9

##
What is the formula for at ?

###
Tangental acceleration

10

## ar is directly proportional to

### V^2

11

## ar is inversly proportional to

### r

12

## Radial Force

###
- Analogous to linear force

- Fr = m x ar

13

##
Since ar = V2/r, the formula for Fr can be re-written as follows:

###
Fr = mV2/r

14

##
Consider this runner negotiating the curve in the track, what factors are of importance?

###
1. The amount of force placed on the lower extremity muscles to stay on the curved path, ie. avoid going off at a tangent to the curve.

2. The angle of lean.

15

##
When considering force: Can you list the 3 factors that would determine the force experienced on the lower extremity muscles when running around a curve?

Start with the formula.

###
Fr = mV2/r

16

## First factor:

###
- Fr is directly proportional to the mass of the runner.

- This means the heavier the runner the Greater the radial force and need to work harder

17

## Second factor: Fr is directly proportional to the ________ of the velocity

###
V^2

- This means the faster the running speed the greater the radial force

18

## Third factor:

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Fr is inversly proportional to the radius of the curve.

- This means that the larger the radius of the track, the less radial force

19

##
The angle of lean

###
This is the angle at which the runner in this case has to tilt when measured from the vertical.

20

##
If AB is the force acting on the lower extremity,

what is the radial force Fr?

what is the force acting at right angles to Fr?

###
The radial force (Fr) is: AD - the force keeping the runner on the track.

21

##
For the angle of lean,

###
Tan Theta = mV2/r divided by mg

Tan Theta = V2 /rg

22

## Therefore the angle of lean is dependent on two factors:

###
- The velocity of the runner.

- The radius of the curve around which the runner moves.

- This is because the other factor, gravity, will not change during the course of the performance.

23

## first factor of the angle of lean

###
It is directly proportional to the square of the velocity of the runner.

Tan Theta directly proportional V2

- This means the faster the runner the angle of lean is more

24

## second factor of the angle of lean

###
It is inversly proportional to the radius of the curve.

Tan Theta is directly proportional 1/r

25

## the second factor means the greater the curve of the track the

###
Less the angle of lean

26

##
If F sine is equal to “mV2/r”

And F cosine is equal to “mg”

What is the angle of lean?

### CB

27