NTNUJAVA Virtual Physics LaboratoryEnjoy the fun of physics with simulations! Backup site http://enjoy.phy.ntnu.edu.tw/ntnujava/
April 19, 2021, 07:49:05 am
 Welcome, Guest. Please login or register.Did you miss your activation email? 1 Hour 1 Day 1 Week 1 Month Forever Login with username, password and session length

 Home Help Search Login Register
"Life is the beaty of art, heart, and humanity."...Wisdom

 Pages: [1]   Go Down
 Author Topic: Friction force vs external force  (Read 13879 times) 0 Members and 1 Guest are viewing this topic. Click to toggle author information(expand message area).
Fu-Kwun Hwang
Administrator
Hero Member

Offline

Posts: 3086

 « Embed this message on: June 25, 2013, 02:54:21 pm »

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 742 times.) Logged
Fu-Kwun Hwang
Administrator
Hero Member

Offline

Posts: 3086

 « Embed this message Reply #1 on: June 26, 2013, 08:04:59 am »

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. $(m+m_2)g\mu : block A and block B move together
($\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)
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!
 springFriction2013.jpg (7.12 KB, 798x202 - viewed 603 times.) Logged
RUPESH BABU
Newbie

Offline

Posts: 4

 « Embed this message Reply #2 on: July 24, 2013, 08:39:23 am »

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
 Logged
Fu-Kwun Hwang
Administrator
Hero Member

Offline

Posts: 3086

 « Embed this message Reply #3 on: July 24, 2013, 08:51:52 am »

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

 « Embed this message Reply #4 on: July 25, 2013, 09:22:40 am »

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. -->
 Logged
Fu-Kwun Hwang
Administrator
Hero Member

Offline

Posts: 3086

 « Embed this message Reply #5 on: July 25, 2013, 06:24:21 pm »

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

 « Embed this message Reply #6 on: July 26, 2013, 09:44:55 pm »

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: 3086

 « Embed this message Reply #7 on: July 27, 2013, 05:48:46 pm »

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

 « Embed this message Reply #8 on: September 12, 2013, 09:08:36 am »

"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
"Life is the beaty of art, heart, and humanity."...Wisdom
Jump to:

 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 14 30451 January 29, 2021, 02:21:57 am by AndrewRoss Relation between friction force, external force, normal force Dynamics Fu-Kwun Hwang 1 16007 July 23, 2009, 04:01:38 pm by lookang Normal force and Friction force dynamics ahmedelshfie 5 14709 September 24, 2010, 07:03:29 pm by ahmedelshfie Relation between friction force, external force, normal force dynamics ahmedelshfie 0 5298 April 22, 2010, 06:53:20 pm by ahmedelshfie relation between friction force and normal force Dynamics Fu-Kwun Hwang 1 10182 June 29, 2013, 03:17:55 pm by Fu-Kwun Hwang
Page created in 1.955 seconds with 23 queries.since 2011/06/15