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Force and Energy
Name: Jeremy C.
Status: student
Age: 18
Location: N/A
Country: N/A
Date: 6/23/2004
Question:
I understand that some form of energy needs to be
converted to create a force. When I push against a wall, where does the
wall get the energy needed to create the reaction force of that contact+
Replies:
Jeremy,
The wall gets the energy from the electromagnetic potential energy stored in
the bonds between the wall's molecules. Also, energy is not required to
create a force. A transfer of energy is required to cause that force to do
work.
Energy is a strange thing in that there is no definite way to define zero
energy. It all depends on what you call zero velocity and what you call the
origin (e.g. zero height for gravity). If you call the surface of a table
zero height, an object on the table has zero gravitational potential energy.
Still, gravitational force can make the object break a weak table and then
cause the object to move downward.
It is difficult to say whether potential energy causes force or vice versa.
Potential energy seems to be stored in the force between objects. If a
force causes an object to speed up, potential energy in the force becomes
kinetic energy in the object. If a force causes the object to slow down,
the reverse occurs. If a force only causes the object to change direction,
there is no transfer of energy. The force causes the transfer of potential
energy, but not necessarily its existence. We do not really know the answer
to that question.
Ken Mellendorf
Math, Science, Engineering
Illinois Central College
The repulsive energy arises from trying to force molecules to occupy the
same space at the same time.
Vince Calder
Jeremy,
There is a slight misunderstanding here. Energy is required to move
against a force. There are forces in nature, such as gravity, that
exist without converting energy. However, in order to move against the
force due to gravity (perform work) some amount of energy needs to be
transferred to gravitational potential energy (energy related to position in a
gravitational field).
So, while you may be expending a lot of chemical energy in pushing
against a wall you are not doing any work on the wall. The wall is not doing any
work in pushing back against you and is not expending any energy. The
wall is being a lot more efficient than you are :- ).
Greg Bradburn
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Update: June 2012
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