The Physics of the Deadlift
Like the Bench Press and Squat, the reason the Deadlift is so effective
to because of gravity. And also like the squat and deadlift, the lifter
does work when lifting the weights.
Now we will talk about the all important physical concept of Conservation
of Energy. Energy can be defined the capacity an object has for performing
work. The law of conservation of energy states:
Energy can neither be created or destroyed. Energy may be transformed
from one from to another, but the total energy of an isolated system is
always constant.
There are many different kinds of energy, such as thermal energy(heat),
nuclear energy, etc. The two kinds we will be concerned with are the gravitational
potential energy and kinetic energy. Gravitational potential
energy U can be defined as the product of the magnitude of the of gravitational
force mg acting on an object and the height y of the object or in equation
form:
U = mgy
Kinetic energy K is the energy of motion. It can be defined by the equation:
K = (1/2)MV^2
The total mechanical energy E of a system is defined as the sum of all
the potential and kinetic energies, so:
E = K + U = (1/2)MV^2 + mgy
If energy is conserved in a system, the total initial energy must equal
the total final energy, so:
Ki + Ui = Kf + Uf
(www.powerlifting-ipf.com
Let's put this law to work in the deadlift. Say the lifter in the picture
is going to lift a mass of 350 kg to a height of a little over 2 meters.
If energy is conserved in the system, and the lifter starts from rest,
what is the velocity of the bar right before the weight reaches the top?
To do this problem, we have to assume that the velocity of the bar is
constant. If the bar starts from rest, initial potential energy is 0 because
y = 0. Initial kinetic energy is also 0 because the weight starts from
rest. So the equation to find the final velocity is:
0 = (1/2)MV^2 + mgy
v^2 = 2gy
v = 6.26 m/s
The velocity of the bar right before it gets to the top is 6.26 meters
per second. This however, is only accurate because we assumed that energy
was conserved in the system. In real life we would have to account for
energy lost to heat and chemical energy from the lifter.
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