Punching and Getting Punched
Even in the sport of boxing, physics can be seen in all aspects of the game.
However, we will be looking at how physics can help a boxer in both throwing a punch,
and taking a hit to the face!
Starting the Punch
When the fighter has his hands in
their initial “ready” positions, his fists have
potential energy originating from muscles and
various bodily functions. As soon as the boxer
starts to move his shoulders and arms and
eventually the fists, his/her potential energy is
being converted into kinetic energy.
Kinetic energy is calculated by using the formula:
Kinetic Energy = (1/2)mv^2
where m is the mass of the object, in this case the arm, fist, and boxing glove, and v is
the velocity of the object.
Contact with the Face and Aftermath
The fist has its maximum velocity when
it hits something. This collision causes the fist to
slow down, and eventually when the fighter
begins applying a force to retract his arm, the fist
stops and returns to the fighter.
This speed is calculated using;
Velocity = Distance / Time
As you can see, there are two ways to make a fist go faster. By lengthening the
distance or shortening the time. The distance can be lengthened to a maximum of the
fighter’s arm length, but the time will depend on training, and the acceleration (a=v/t) of
the arm.
But what is the advantage to a “faster” punch? We can investigate this by taking
a look at the concepts of momentum and impulse. Momentum can be seen as an object’s
tendency to resist change in acceleration and its formula is:
Momentum (P) = Mass * Velocity
An impulse is the change in momentum of a certain object, and uses the formula:
Impulse = Force * Time
Now what does this have to do with boxing? Well, this becomes more evident
when looking at the punch in steps:
1. Before the fist makes contact with the face, it has a certain momentum, and a
stationary head would have zero momentum.
2. During the contact, there is a transfer of momentum from the fist and arm to the
head of the opponent.
3. Although momentum is conserved when looking at both boxers, just looking at
the person taking hit, his/her momentum has changed from zero, to what ever
momentum was transferred from the fist.
To return to the question of why a faster punch can be more effective is because with the
mass of the fist being constant, by increasing velocity, the momentum that the punch
carries is larger, hence, but change in momentum (impulse) that the opponent’s head
experiences increases.
During contact,
the boxer taking the
hit would experience
the same impulse
whether his/her head
is moving towards the
punch, or moving away from it. It is important to understand
that this doesn’t mean that the boxer would feel the same
impulse if he/she was moving towards the punch before the
fist made contact with his/her face, it must be after contact is
made. Even though the impulse, or change in momentum,
experienced would be the same for both cases, by moving
Force Time
Impulse
200
1
200
100
2
200
50
4
200
20
10
200
8
25
200
4
50
200
2
100
200
0.2
1000
200
the head away from the punch increases the time interval in which the “damage” takes
place, meaning the force experienced from taking the punch will be reduced. Since it
only takes a boxer a fraction of a second to throw a punch, a small reduction in the time
interval can produce large results.
As you can see, the simple basic punching in boxing involves many physics
concepts. By knowing these concepts, the boxers can know what aspects of their offense
and defensive abilities need training, and we can have a more scientific approach to the
sport.