Why is it necessary to bend knees while jumping from a height?
Asked Rahul. (via SMS from our mobile version http://m.askphysics.com )
This is a consequence of the impulse momentum principle.
When we bent our knees on landing, the time of impact increases and reduces the average force exerted during the entire process. This prevents the chance of damage to our body.
Impulse momentum principle states that the impulse of a force is equal to the change in momentum produced.
Impulse is measured as the product of force and time interval. So, when we stop ourselves, there is a fixed change in momentum. If we stop ourselves very fast, the time interval is less and the average force will be very large.
But, if we bent our knees during landing, the time involved in the proces of landing will be more and thus the average force will be less and hence the damage will also be less.
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
“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.
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!