Newton's Laws

What is the first law?

An object at rest tends to stay at rest and an object in motion tends to stay in motion

with the same speed and in the same direction unless acted upon by an

unbalanced force.

What is inertia?

The natural tendency of objects to resist changes in

their state of motion.

Do balanced or unbalanced forces affect an object's state of inertia?

Both!

Balanced forces act to keep an object in place so there is no change in motion. For example, the force of gravity pulling down on a book and the force of the table pushing up on a book are equal. These two forces balance each other so the object remains at rest.

Unbalanced forces cause changes in an object’s state of motion (inertia is disrupted). The book is not at equilibrium and so it causes it to change (book goes from resting to moving or from moving to resting).

What is the second law?

The second law states that the acceleration of an object is dependent upon two variables (force and

mass).

Force increases whenever there is an increase in mass and/or acceleration.

What is the formula that originated from the second law?

Force = mass x accelerationF = m x a

What unit is force measured in?

Newtons (N)

Newtons are just kg x m/s2

Show all the work and use the correct units!!!

1.) A 50kg skater pushed by a friend accelerates 5m/s2. How

much force did the friend apply?

Force = mass x acceleration

Force = 50kg x 5m/s2

Force = 250.0kg●m/s2 = 250N

2.) If a 60kg person on a 15kg sled is pushed with a force of 300 Newtons, what will be the

person's acceleration?

Acceleration = force mass

Acceleration = 300kgkg●m/s2

75kg

Acceleration = 4.0m/s2

3.) A bowling ball rolled with a force of 15 Newtons accelerates at a rate of 3m/s2. What is the

mass of the ball?

Mass = Force Acceleration

Mass = 15kg●m/s2 3m/s2

Mass = 5.0kg

Newton's 3rd Law

What is the third law?

For every action there is an equal and opposite reaction.

Or in other words, every force must have an equal and opposite force!

Thus, all forces come in PAIRS!

Below the diagram in your notes, explain Below the diagram in your notes, explain using Newton's third law why the boy will using Newton's third law why the boy will

end up in the water.end up in the water.

As the boy pushes forward to step onto the dock, the boat pushes back and is shifted backwards. Now let's check out how this

might work in our own little situation.

Describe your own examples of Newton's Third Law:

1.) Walking – your foot pushes against the ground and the ground pushes

back and you move forward while the Earth moves in the opposite direction.

2.) Trampoline – as you push down on the trampoline, the trampoline pushes back

against your feet and is able to launch you in the air.

3.) Water sprinkler – the water pushes out of the spouts in one direction which forces

the arm of the sprinkler to spin in the opposite direction