Download 3 laws - NCEA-Physical

Biomechanics
Laws
Today’s session will cover

Newton’s laws of motion.

First Law – Inertia

Second Law - Acceleration & Momentum

Third Law - Equal & Opposite
Newton’s First Law

An object at rest tends to remain at rest
unless acted upon by some external force.
Known as Inertia.
 Basically inertia is an objects resistance to
move.
 Which is harder to move?

Having a great deal of inertia can be
advantageous in some sporting situations.
How?
If you have a lot of inertia you can be
difficult to move. E.g. a rugby scrum,
wrestling, judo
 Of course having a lot of inertia has
disadvantages as well in sporting situations.
How?
If you have a lot of inertia you require a lot
of force or effort to get you moving. It can
also mean decreased agility.
Newton’s Second Law

When a force acts upon a mass, the result is
acceleration of that mass.
 Student example

Force = Mass x Acceleration
 F = MA

If each is hit or bowled with the same
amount of force, which one accelerates the
most? Why?
The table tennis ball because it is lighter.
 If the tennis ball is hit with gradually
increasing force, what happens to its
acceleration?
The acceleration will increase with
increasing force.
Summary of 2nd law

The greater the force, the greater the acceleration.
 The smaller the mass, the greater the acceleration
when a constant force is applied.
 The mass will accelerate in the direction the force
is applied.
 How could you apply Newton’s 2nd law in a
sporting situation.
Newton’s Third Law

For every action, there is an equal and
opposite reaction.

“What goes up, must come down”
Summary of 3rd law

When we apply a force to something, this is
known as a action force.

The object we apply a force to, applies a
force back, a reaction force.

What other example of this can you think
of? When a ball is bounced, it bounces
back in a direction opposite to that in which
it was dropped.
 If these forces are equal, why is the earth
not pushed backward when we drive out of
the starting blocks in a 100 metre race?
The earth has a huge mass and therefore
huge inertia. We cannot generate enough
force to overcome this inertia.