Newton’s Laws of Motion

Conservation Laws in

Astronomy

Isaac Newton1642 (1643) - 1727

Isaac Newton1642 (1643) - 1727

Invented calculus

Isaac Newton1642 (1643) - 1727

Invented calculus

Studied optics

Isaac Newton1642 (1643) - 1727

Invented calculus

Studied optics

Developed his law of universal gravitation

Newton’s First Law of Motionis also known simply as

“Inertia”

Galileo actually came up with it first.

If there is no net force on an object

a) it doesn't move.

b) its velocity doesn't change.

c) its momentum doesn't change.

d) all of the above

e) b and c

Acceleration is any change in motion

m

Fa

maF

maF m

Fa

A 7.5 N force acts on a 12.5 kg satellite when its thruster fires. What will its acceleration be?

maF m

Fa

As you watch, a 12,000 kg F-16 fighter jet accelerates through the air at 10.6 m/s2. What is the thrust of its engine?

A ball is swung around in circles on a string. Is there a net force on the ball?

A) Yes

B) No

C) It’s not possible to decide without further information.

In this case, the force is always perpendicular to the velocity.

That force will change the direction without changing the speed.

Remember:If velocity changes, there is ALWAYS a non-zero net force.

Newton’s Third Law of Motion

When object 1 exerts a force on object 2, object 2 exerts the SAME force on object 1, but in the opposite direction

Sometimes called “Action – Reaction”

Equal and opposite force pairs

Newton’s Third Law of Motion

Working in space is complicated by Newton’s third law

Newton’s Law Summary

Inertia F = ma Action-Reaction

1 2 3

An astronaut on a space walk outside the International Space Station finds herself 20 m away from the station, sitting perfectly still (with respect to the ISS), with no tether, and her hand-held maneuvering gun is out of fuel. How can she get back to the ISS?

A) She can’t – she’s space toast

B) Throw the maneuvering gun directly away from the ISS

C) Throw the maneuvering gun directly at the Earth

D) Throw the maneuvering gun directly at the ISS

E) Make a swimming motion toward the ISS

Conservation of Momentum

If the net external force on a system is zero, there will be no change in the

system’s momentum.

It takes an external force to change the momentum

of a system.

What external force gave this system its momentum?

Conservation of Angular Momentum

The type of force that can change an object’s angular momentum is called “torque”

Torque is force x distance

Using a wrench increases torque by increasing distance

distance

force

Conservation of Angular Momentum

This has an interesting effect on spinning objects…

Note that there is no net torque on the skater

Her angular momentum is NOT changing

Astro-Cash Cab!

Adrianna Cordova

Tyler Zito

Corey Schatz

Pauline Luhman

Derek DiThomas

1) If a planet travels in a circular orbit without speeding up or slowing down, does it have a force on it?

2) True or False ?

Newton’s First Law of Motion says that the planets travel around the Sun in ellipses, with the Sun at one focus.

3) If a 10 kg object is acted on by a 100 N force, what will its acceleration be?

4) What conservation law explains why a rotating skater speeds up when she pulls her arms in?

Conservation of Energy

Conservation of Momentum

Conservation of Angular Momentum

Conservation of Charge