Turning Effect of Forces
-
Upload
josiah-evans -
Category
Documents
-
view
39 -
download
0
description
Transcript of Turning Effect of Forces
![Page 1: Turning Effect of Forces](https://reader036.fdocuments.in/reader036/viewer/2022062321/56812bd1550346895d9032ff/html5/thumbnails/1.jpg)
![Page 2: Turning Effect of Forces](https://reader036.fdocuments.in/reader036/viewer/2022062321/56812bd1550346895d9032ff/html5/thumbnails/2.jpg)
MOMENTS
What is moments?
A force can cause many things to move or stop. When a force causes an object to turn, this turning effect is called moments.
Example: A person sitting on a see-saw.
![Page 3: Turning Effect of Forces](https://reader036.fdocuments.in/reader036/viewer/2022062321/56812bd1550346895d9032ff/html5/thumbnails/3.jpg)
Types Of Moments
There are 2 types moments:
Clockwise moment
Anticlockwise moment
![Page 4: Turning Effect of Forces](https://reader036.fdocuments.in/reader036/viewer/2022062321/56812bd1550346895d9032ff/html5/thumbnails/4.jpg)
Everyday Examples
1. turning a door knob
2. opening a door
3. scissors
4. turning a steering wheel
5. crane at the construction sites lifting objects
6. electrical fan
![Page 5: Turning Effect of Forces](https://reader036.fdocuments.in/reader036/viewer/2022062321/56812bd1550346895d9032ff/html5/thumbnails/5.jpg)
Everyday Examples
7. spanner & nut
![Page 6: Turning Effect of Forces](https://reader036.fdocuments.in/reader036/viewer/2022062321/56812bd1550346895d9032ff/html5/thumbnails/6.jpg)
Everyday Examples
7. 8. Wheelbarrow
![Page 7: Turning Effect of Forces](https://reader036.fdocuments.in/reader036/viewer/2022062321/56812bd1550346895d9032ff/html5/thumbnails/7.jpg)
Activity
Stand up and support your bag with your wrist.
Straighten your hand. Lift it up slowly until it is perpendicular to your body.
Is it easy to do that?
Hang the bag at your elbow and repeat the motion.
How do you feel now? How do you think the distance between the pivot and the force affect the moments?
![Page 8: Turning Effect of Forces](https://reader036.fdocuments.in/reader036/viewer/2022062321/56812bd1550346895d9032ff/html5/thumbnails/8.jpg)
Activity
Stand up and support your bag with your wrist.
Straighten your hand. Lift it up slowly until it is perpendicular to your body.
Ask your partner to remove some books from your bag.
How do you feel as the books are removed?
What does it tell you about the relationship between force and moments?
![Page 9: Turning Effect of Forces](https://reader036.fdocuments.in/reader036/viewer/2022062321/56812bd1550346895d9032ff/html5/thumbnails/9.jpg)
What does the turning effect of a force depend on?
1. force
2. perpendicular distance between force and pivot
![Page 10: Turning Effect of Forces](https://reader036.fdocuments.in/reader036/viewer/2022062321/56812bd1550346895d9032ff/html5/thumbnails/10.jpg)
Your turn!
Try out the question in the notes on how you should hang your clothes on a bamboo.
![Page 11: Turning Effect of Forces](https://reader036.fdocuments.in/reader036/viewer/2022062321/56812bd1550346895d9032ff/html5/thumbnails/11.jpg)
Turning Effect of a Force
Note: turning effect = moment = torque
The moment of a force is its turning effect about a pivot
![Page 12: Turning Effect of Forces](https://reader036.fdocuments.in/reader036/viewer/2022062321/56812bd1550346895d9032ff/html5/thumbnails/12.jpg)
Turning Effect of a Force
Moments is the product of the force and the perpendicular distance from the pivot to the line of action of the force.
d
![Page 13: Turning Effect of Forces](https://reader036.fdocuments.in/reader036/viewer/2022062321/56812bd1550346895d9032ff/html5/thumbnails/13.jpg)
CALCULATING MOMENTSCALCULATING MOMENTS
Moment = force perpendicular distance between force and pivot
In symbols: Moments = F d
Weight => F
d
Unit for moments: Newton-metre (Nm)
![Page 14: Turning Effect of Forces](https://reader036.fdocuments.in/reader036/viewer/2022062321/56812bd1550346895d9032ff/html5/thumbnails/14.jpg)
F = 20N
d = 3m
Example 1:
A cat of weight 20N stands on one end of a see-saw and the distance between the cat and the pivot is 3m, find the moment.
Solution: In this case the cat is causing a clockwise moment.
Clockwise moment = F x d
= 20 x 3
= 60 Nm
Worked Example 1
![Page 15: Turning Effect of Forces](https://reader036.fdocuments.in/reader036/viewer/2022062321/56812bd1550346895d9032ff/html5/thumbnails/15.jpg)
Example 2:
A duck stands on one end of a see-saw, 5m away from the pivot. If the weight of the duck is 10N, find the moment.
Solution: The duck’s weight is causing an anticlockwise moment.
Anticlockwise moment = F x d
= 10 x 5
= 50 Nm
F = 10N
d = 5m
Worked Example 2
![Page 16: Turning Effect of Forces](https://reader036.fdocuments.in/reader036/viewer/2022062321/56812bd1550346895d9032ff/html5/thumbnails/16.jpg)
Try out the questions in the notes to find the moments caused by the force
Your turn!
![Page 17: Turning Effect of Forces](https://reader036.fdocuments.in/reader036/viewer/2022062321/56812bd1550346895d9032ff/html5/thumbnails/17.jpg)
It is easy to balance two objects of It is easy to balance two objects of the same weightthe same weight
Anticlockwise moment
Anti- clockwise moment
• Anticlockwise moment
• Clockwise moment
![Page 18: Turning Effect of Forces](https://reader036.fdocuments.in/reader036/viewer/2022062321/56812bd1550346895d9032ff/html5/thumbnails/18.jpg)
Is it possible to balance a objects of Is it possible to balance a objects of different weight?different weight?
![Page 19: Turning Effect of Forces](https://reader036.fdocuments.in/reader036/viewer/2022062321/56812bd1550346895d9032ff/html5/thumbnails/19.jpg)
weight weight
Principle of Moments
For an object to be in equilibrium(stable/not moving), the total clockwise moment must be equal to the anticlockwise moment about the same pivot.
pivotIt is the fixed(non moving) point
![Page 20: Turning Effect of Forces](https://reader036.fdocuments.in/reader036/viewer/2022062321/56812bd1550346895d9032ff/html5/thumbnails/20.jpg)
SOLVING PROBLEMS RELATED TO PRINCIPLE OF MOMENTS
Step 1:
Identify what are the forces that will give rise to clockwise / anticlockwise moment
Step 2:
Find the clockwise / anticlockwise moment
Step 3:
Equate the clockwise and anticlockwise moments
![Page 21: Turning Effect of Forces](https://reader036.fdocuments.in/reader036/viewer/2022062321/56812bd1550346895d9032ff/html5/thumbnails/21.jpg)
10N30N
6m d
Find the value of d.
Worked Example 3
![Page 22: Turning Effect of Forces](https://reader036.fdocuments.in/reader036/viewer/2022062321/56812bd1550346895d9032ff/html5/thumbnails/22.jpg)
Step 1:
Identify what are the forces that will give rise to clockwise / anticlockwise moment
![Page 23: Turning Effect of Forces](https://reader036.fdocuments.in/reader036/viewer/2022062321/56812bd1550346895d9032ff/html5/thumbnails/23.jpg)
10N
30N
6m d
Find the value of d.
Anticlockwise moment
Clockwise moment
Worked Example 3
![Page 24: Turning Effect of Forces](https://reader036.fdocuments.in/reader036/viewer/2022062321/56812bd1550346895d9032ff/html5/thumbnails/24.jpg)
Step 2:
Find the clockwise / anticlockwise moment
![Page 25: Turning Effect of Forces](https://reader036.fdocuments.in/reader036/viewer/2022062321/56812bd1550346895d9032ff/html5/thumbnails/25.jpg)
10N
30N
6m d
Clockwise moment = Force x distance between force and pivot
= 30 x d = 30d Nm
Anticlockwise moment
Clockwise moment
Anticlockwise moment = Force x distance between force and pivot= 10 x 6= 60 Nm
Find the value of d. Solution:
Worked Example 3
![Page 26: Turning Effect of Forces](https://reader036.fdocuments.in/reader036/viewer/2022062321/56812bd1550346895d9032ff/html5/thumbnails/26.jpg)
Step 3:
Equate the clockwise and anticlockwise moments
![Page 27: Turning Effect of Forces](https://reader036.fdocuments.in/reader036/viewer/2022062321/56812bd1550346895d9032ff/html5/thumbnails/27.jpg)
10N
30N
6m d
Find the value of d. Solution: Clockwise moment = Force x distance between force and
pivot= 30 x d= 30d Nm
Anticlockwise moment = Force x distance between force and
pivot= 10 x 6= 60 Nm
Using the principle of moments, Clockwise moment = Anti-clockwise moment
30d = 60d = 60 30d = 2 m
Anticlockwise moment
Clockwise moment
Worked Example 3
![Page 28: Turning Effect of Forces](https://reader036.fdocuments.in/reader036/viewer/2022062321/56812bd1550346895d9032ff/html5/thumbnails/28.jpg)
Points to note:
1.The unit for force must be in Newtons, the unit for distance must be in metres.
2.The distance must measured perpendicularly from the force to the pivot.
![Page 29: Turning Effect of Forces](https://reader036.fdocuments.in/reader036/viewer/2022062321/56812bd1550346895d9032ff/html5/thumbnails/29.jpg)
The figure shows a uniform rod of length 4 m and weight 50N. It is pivoted at Q. A boy tries to lift up the rod vertically from the end P. What is the magnitude of the force when P is just lifted ?
rodQ4m
Force, F
P
50 N
Worked Example 4
![Page 30: Turning Effect of Forces](https://reader036.fdocuments.in/reader036/viewer/2022062321/56812bd1550346895d9032ff/html5/thumbnails/30.jpg)
The figure shows a uniform rod of length 4 m and weight 50N. It is pivoted at Q. A boy tries to lift up the rod vertically from the end P. What is the magnitude of the force when P is just lifted ?
Solution
When the body is in equilibrium,
F x 4m = 50N x 2m F = 25 N
rodQ4m
Force, F
P
50 N
Worked Example 4
![Page 31: Turning Effect of Forces](https://reader036.fdocuments.in/reader036/viewer/2022062321/56812bd1550346895d9032ff/html5/thumbnails/31.jpg)
The light ruler in the figure shown below is balanced. Calculate
(a) the value of W
(b) the normal reaction at the pivot P.
W 4N 1NP
20cm 15 cm 25 cm
Worked Example 5
![Page 32: Turning Effect of Forces](https://reader036.fdocuments.in/reader036/viewer/2022062321/56812bd1550346895d9032ff/html5/thumbnails/32.jpg)
The light ruler in the figure shown below is balanced. Calculate
(a) the value of W
(b) the normal reaction at the pivot P.
Solution
(a) When the body is in equilibrium,
(Wx20cm) = (4Nx15cm) + (1Nx40cm)
therefore W = 5N
(b) Normal reaction at P = (5 + 4 + 1) = 10 N
W 4N 1NP
20cm 15 cm 25 cm
Worked Example 5
![Page 33: Turning Effect of Forces](https://reader036.fdocuments.in/reader036/viewer/2022062321/56812bd1550346895d9032ff/html5/thumbnails/33.jpg)
Your turn!
Try out the question in the notes on principle of moments