Friction force vs external force

Fu-Kwun Hwang

Administrator
Hero Member

Offline

Posts: 3085

1 Friction force vs external force

Embed this message

on: June 25, 2013, 02:54:21 pm » posted from:Taipei,T'ai-pei,Taiwan

A block with mass $m$ is put on top of a surface. The friction coefficient between block and the surface is $\mu$ .
The normal force is $m g$ , so the maximum static friction $F_\mu\le m g \mu$ .
It means when the external force is less than $m g$ , the friction force is $- m g$ .
However, if the external is larger than the maximum static friction force then the friction force stay constant $- mg \mu$ .
And the block starts to move.
The following simulation let you play with the above case.
You can drag the spring horizontally to change the external force.

CLick the following image to display the simulation.

Embed a running copy of this simulation

Embed a running copy link(show simulation in a popuped window)

Full screen applet or Problem viewing java?Add http://www.phy.ntnu.edu.tw/ to exception site list
Press the Alt key and the left mouse button to drag the applet off the browser and onto the desktop. This work is licensed under a Creative Commons Attribution 2.5 Taiwan License

Please feel free to post your ideas about how to use the simulation for better teaching and learning.
Post questions to be asked to help students to think, to explore.
Upload worksheets as attached files to share with more users.

Let's work together. We can help more users understand physics conceptually and enjoy the fun of learning physics!

springFriction20130.jpg (25.48 KB, 762x290 - viewed 683 times.)
	Logged

Fu-Kwun Hwang

Administrator
Hero Member

Offline

Posts: 3085

2 Re: Friction force vs external force

Embed this message

Reply #1 on: June 26, 2013, 08:04:59 am » posted from:,,Satellite Provider

Here is another more complicated version.

Bock A with mass m is put on top of a surface. There is another block (B) with mass m2 on top of block A.
Friction coefficient between block A and surface is $\mu$ , between block A and block B is $\mu_2$ .

The normal force between block A and surface is $(m+m_2) g$ , between block A and block B is $m_2 g$
The external force is F:

1. $F\le (m+m_2)g \mu$ : both block would not move
Friction force between block A and surface is $-F$ , between block A and block B is 0.
2. $(m+m_2)g\mu<F\le (m+m_2) g (\mu+ \mu_2)$ : block A and block B move together
( $\frac{F-(m+m_2)g\mu}{m+m2}m_2< m_2 g\mu_2$ Force on block B less than maximum static friction force)
Friction force between block A and surface is $(m+m_2)g \mu$ , acceleration of both blocks is $\frac{F-(m+m_2) g\mu}{m+m2}=\frac{F}{m+m_2}-g\mu$
friction force between block A and block B is $\frac{m_2}{m+m_2} (F-(m+m_2) g\mu)=\frac{m_2}{m+m_2}F-m_2 g \mu$
3. $F>(m+m_2) g (\mu+\mu_2)$ : block A and block B move separately.
Friction force between block A and surface is $(m+m_2)g \mu$ , acceleration of blocks A is $\frac{F-(m+m_2) g\mu-m_2 g\mu_2}{m}$
friction force between block A and block B is $m_2 g \mu_2$ , acceleration of block B is $g \mu_2$

Enjoy the simulation!
CLick the following image to display the simulation.

Embed a running copy of this simulation

Embed a running copy link(show simulation in a popuped window)

Please feel free to post your ideas about how to use the simulation for better teaching and learning.
Post questions to be asked to help students to think, to explore.
Upload worksheets as attached files to share with more users.

Let's work together. We can help more users understand physics conceptually and enjoy the fun of learning physics!

springFriction2013.jpg (7.12 KB, 798x202 - viewed 568 times.)
	Logged

RUPESH BABU

Newbie

Offline

Posts: 4

3 Re: statics and dynamics

Embed this message

Reply #2 on: July 24, 2013, 08:39:23 am » posted from:Pondicherry,Puducherry,India

please, help me..!
differentiate between
1. Body at rest which has no net force
2. Body moving at constant velocity which has no net force Sad


	Logged

Fu-Kwun Hwang

Administrator
Hero Member

Offline

Posts: 3085

4 Re: statics and dynamics

Embed this message

Reply #3 on: July 24, 2013, 08:51:52 am » posted from:Taipei,T'ai-pei,Taiwan

A person sit on a car moving with constant velocity.

For observer in the same car: that person is at rest which has no net force.
For observer at rest relative to the ground: that person is moving at constant velocity(the same as the car) which has no force.


	Logged

RUPESH BABU

Newbie

Offline

Posts: 4

5 Re: statics and dynamics

Embed this message

Reply #4 on: July 25, 2013, 09:22:40 am » posted from:Pondicherry,Puducherry,India

parameters :
velocity = 0 , final velocity = v ;
acceleration = 0 , acc_mid = a [from 0 to v] , final acceleration = 0 ;

concept:
1. Initially ,velocity is zero.
2. Force is applied to reach constant velocity (i.e) to overcome friction and to accelerate , producing net force.
3. After reaching velocity 'v' , net force is zero. (i.e) force is applied only to overcome friction.

My understandings says that, at CONSTANT VELOCITY,
FORCES are there , only NET FORCE is zero.
If my concept is right then acknowledge me else help me with CORRECT concept...

SIR, many questions are with me. I want to get clarified one by one. Here after ,you can see my posts frequently. Huh

-->


	Logged

Fu-Kwun Hwang

Administrator
Hero Member

Offline

Posts: 3085

6 Re: Friction force vs external force

Embed this message

Reply #5 on: July 25, 2013, 06:24:21 pm » posted from:,,Satellite Provider

Yes. Net force is zero when an object move with constant velocity.
The external is required if there are friction force or other kind of force resist the motion of the object.


	Logged

RUPESH BABU

Newbie

Offline

Posts: 4

7 Re : mechanics

Embed this message

Reply #6 on: July 26, 2013, 09:44:55 pm » posted from:Pondicherry,Puducherry,India

What is moment of inertia ?
- polar moment of inertia ?
Please explain the term briefly with its importance in dynamics with real time examples.
please brief brief.....


	Logged

Fu-Kwun Hwang

Administrator
Hero Member

Offline

Posts: 3085

8 Re: Friction force vs external force

Embed this message

Reply #7 on: July 27, 2013, 05:48:46 pm » posted from:,,Satellite Provider

Please check out wikipedia first.

You are welcomed to post in more detail what you do not understand and we will try to help.
But you should learn to check out information by yourself.


	Logged

RUPESH BABU

Newbie

Offline

Posts: 4

9 Re: MEchanics

Embed this message

Reply #8 on: September 12, 2013, 09:08:36 am » posted from:Pondicherry,Puducherry,India

"Moment of Inertia or (Polar I) is the tendency to resist the rotational motion".
this is the fact I grabbed...
But I need some insight meaning related statics as well as dynamics...(ie. about its role in these areas).
PLease be brief.! that will help me a lot


	Logged

Pages: [1] Go Up

"Make priority, take action and start now." ...Wisdom

« previous next »

Related Topics
	Subject	Started by	Replies	Views	Last post
	Ski as example to illustrate the friction force (normal force...etc) Request for physics Simulations	Fu-Kwun Hwang	12	29153	August 24, 2011, 12:19:16 pm by melody
	Relation between friction force, external force, normal force Dynamics	Fu-Kwun Hwang	1	15449	July 23, 2009, 04:01:38 pm by lookang
	Normal force and Friction force dynamics	ahmedelshfie	5	14409	September 24, 2010, 07:03:29 pm by ahmedelshfie
	Relation between friction force, external force, normal force dynamics	ahmedelshfie	0	4993	April 22, 2010, 06:53:20 pm by ahmedelshfie
	relation between friction force and normal force Dynamics	Fu-Kwun Hwang	1	9903	June 29, 2013, 03:17:55 pm by Fu-Kwun Hwang

	Author	Topic: Friction force vs external force (Read 13545 times)
0 Members and 1 Guest are viewing this topic. Click to toggle author information(expand message area).