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What is centripetal force?

What is centripetal force?
Received via SMS from our mobile version of this site http://m.askphysics.com
Centripetal fforce is the net force to be acting on a body so that it can move in a curved path. The centripetal force is always directed towArds the center of the circular path. The word centripetal means “directed towards the center” or “center seeking force”.
Please remember that it is not a new kind of force, but in different case one or more of the fundamental forces or their components provide the necessary centripetal for e.
The magnitude of the centrifugal force that must be acting on a body of mass m moving with a speed v along a curve of radius of curvature r is given by F = mv^2/r

Pressure, Thrust, Area and Pascal’s Law

“In Pascal’s law we find that pressure does not increase with area. But when we study about pressure, we learn that pressure is inversely proportional to area. How is this possible? Please explain.”

Fahad Imtiaz asked via Speak Pipe



Pressure is defined as the thrust (the total force acting normal to a surface) per unit area.

Pascal’s law deals with fluid pressure and the statement goes –

“The pressure exerted anywhere in an enclosed incompressible and non-viscous fluid is transmitted equally and undiminished in all directions through out the fluid, provided the effect of gravity is neglected”

Read the statement carefully.

Here we are not changing the definition or meaning of pressure.

the fact to note that, in an enclosed fluid, the pressure is transmitted equally throughout the fluid. Therefore, if we apply some pressure somewhere in the fluid, the same pressure will be felt  at any other place on the enclosed fluid. This gives us an opportunity to multiply the force. Since the pressure is equal everywhere, if we increase the area the force (thrust) is increased.

P = F/A or F = PA

So, pressure remaining constant, greater the area, greater is the force.

Hope you understand the matter now.

Force – Impulse – Momentum

Hi All! I’m having mega problems with one part of a physics assignment. Looking for any help.
The details are as follows:

The diagram shows the normal force on Christine’s feet vs. time, as recorded by a force plate while she stands still initially (until point B), then jumps off the plate. (This trial is separate from the one in the previous problem. The graph is over-simplified and idealised, compared to reality.) When her feet leave the plate, the normal force is zero.

1)What is the magnitude of the (upward) impulse generated by the normal force of Christine during the time interval of her jump off the plate?

2)What is the magnitude of the downward impulse due to gravity during this interval?

3)What is the net impulse which propels her upwards when she jumps off the plate? (Recall, the net force on her is the normal force minus the force of gravity.)

4)What is her change in speed upwards for this process?

The graph has NORMAL FORCE (N) on the y-axis and TIME (s) on the X axis.
The line is at a constant 550 N until point B (1.75 seconds) at which time it shoot up vertically to 1550 N at a time of 1.95 seconds. It peaks at this time and position then drops down to 0 N at 2.15 seconds.

Thanks in advance for any guidance that can be provided!


Why there is a 4(pi) in Coulomb’s law?

Why there is a 4π in Coulomb’s law?

Asked Rick Ghosh


This is a consequence of geometry.

Please remember that Coulomb’s law is stated originally for point charges  at rest. By symmetry, a point charge should exert equal force on a test charge at all points equidistant from it, which constitute a spherical shell of surface area 4πr2.

This consideration itself suggests the inverse square relation ship as well as the need for 4π.

That was actually my explanation for it.

The term 4π was not there when Coulomb’s law was first stated in cgs system. The term 4π was introduced in SI on rationalization of units based on Maxwell’s equations of electromagnetism.

But I feel that  my earlier explanation is simple and convincing.

Hope you got it.

Further discussions are welcome.

A problem from Dynamics

The coefficient of kinetic friction between the 2.00-kg and 3.00-kg blocks
is 0.300. The horizontal surface and the pulleys are frictionless, and the masses are released from rest.
a) Draw a free-body diagram for each block.
b) Determine the acceleration of each block.
c) Find the tension in the strings.

Buoyant force

What is buoyant force? I’m unable to understand practically from book. please give vast and practical explanation.. (Raj asked)


Whenever a body is immersed in a fluid, say water, it experiences an upward force acting on it. The upward force exerted by a fluid on an object immersed in it is called Buoyant force.

When an object is immersed, it displaces the fluid already present there. The upward force (buoyant force) is the result of the fluid’s attempt to reoccupy the space.

If the object placed in a fluid is denser than the fluid, it will sink. Though it experiences an upthrust, its weight will be more than the upthrust.

The upthrust is equal to the weight of liquid displaced by the immersed part of the body.

If the object is of less density than the fluid, it will come up and float.

For a floating body, the net weight is equal to zero, as the upthrust balances the actual weight of the body.


The pressure exerted by a given force can be decreased by increasing the area of contact.


The equation shows that pressure is inversely proportional to area.


The foundation off building is made more broader than the rest of the building so that the pressure exerted by the weight on earth can be decreased.



The shoulder straps of school bags are made wider and soft so that the pressure exerted by the heavy bags on shoulders can be reduced. You can feel the paining pressure if you try to replace the broad strap with a narrow one.




The Military tanks have a broad chain so that the pressure exerted by the heavy vehicle on ground is a minimum and it can travel even through marshy places

  • Heavy Vehicles have more tyres
  • When vehicles get struck in marshy places, wooden planks are used for the vehicle to come up.
Try to add more via comments

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Half Yearly Exam Count Down

Half Yearly Exam Count Down KVS Ernakulam RegionOctober 17th, 2017
The Half Yearly Examination for Kendriya Vidyalayas of Kerala starts from 17 October 2017
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