# NTNUJAVA Virtual Physics LaboratoryEnjoy the fun of physics with simulations! Backup site http://enjoy.phy.ntnu.edu.tw/ntnujava/

## Easy Java Simulations (2001- ) => Dynamics => Topic started by: Fu-Kwun Hwang on June 25, 2013, 02:54:21 pm

 Title: Friction force vs external force Post by: Fu-Kwun Hwang 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.[eye][ejsapplet][/eye] Title: Re: Friction force vs external force Post by: Fu-Kwun Hwang 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. $(m+m_2)g\mu ($\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.[eye][ejsapplet][/eye] Title: Re: statics and dynamics Post by: RUPESH BABU on July 24, 2013, 08:39:23 am please, help me..!differentiate between 1. Body at rest which has no net force2. Body moving at constant velocity which has no net force :( :( Title: Re: statics and dynamics Post by: Fu-Kwun Hwang 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. Title: Re: statics and dynamics Post by: RUPESH BABU 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. ??? -->  :) Title: Re: Friction force vs external force Post by: Fu-Kwun Hwang 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. Title: Re : mechanics Post by: RUPESH BABU 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..... :) Title: Re: Friction force vs external force Post by: Fu-Kwun Hwang 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.  Title: Re: MEchanics Post by: RUPESH BABU 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 :)