Intro to Biomechanics (Day 2): Newton's Laws

First Rule of Order: Understanding Physics →
Newton’s Laws

●Newton’s 1st Law (Inertia): An object at rest
remains at rest, and an object in motion remains in
motion at constant speed and in a straight line
unless acted on by an unbalanced force.

●Newton’s 2nd Law (F=ma): the net force acting on
an object is equal to the object's mass multiplied
by its acceleration.

●Newton’s 3rd Law (Action & Reaction): states that
for every action there is an equal and opposite
reaction.

1st Law Analogy and Connection

Think of This:

If you're sitting still, you stay still unless something
pushes or pulls you (like if you’re on a skateboard,
you’ll stay still until you kick the ground to move
forward). Your muscles provide that push in the body’s
case.

●Give me another example

2nd Law Analogy and Connection

Think of This:

This is the one that says force equals mass times acceleration. Imagine you’re
pushing a heavy shopping cart versus a light one. The heavier cart requires more
force to move at the same speed. Similarly, in biomechanics, the muscles provide
the force to move our body, and heavier body parts (like legs) need more force to
move quickly.

●Can you think of another example?!

3rd Law Analogy and Connection

Think of This:

When you jump, you push down on the ground, and the ground pushes back up
with equal force, which launches you into the air. In biomechanics, we look at these
interactions all the time to see how the body reacts to forces in sports, walking, or
any kind of movement.

●What you think? Give me another example???

So How Does This
Apply to My Body
& Movement?!

Think of your muscles as the motors that generate force,
and your bones as the levers that these motors move.

For example, when you lift something with your arm, your
biceps muscle (the motor) pulls on your forearm bone
(the lever). This is just like how a crane lifts heavy
objects—its motor pulls on cables to lift the arm, which
works like a lever.

Questions We May Ask

●How strong the muscle has to be to pull or contract to lift a certain
weight/object?

●How much force the bone can handle before it breaks?

●How fast or smoothly the movement happens?