Laws of Motion Mrs. Wolfe “If I have seen far, it is because I have stood on the shoulders of giants.” - Sir Isaac Newton (referring to Galileo)

What is Force? Fkick Fgrav Force a push or pull that one object exerts on another What forces are being exerted on the football? Fkick Fgrav

Draw a diagram showing the forces… A girl is hanging from a bar held from the ceiling by two ropes.

Draw a diagram of … A flying squirrel is gliding from a tree to the ground.

Try one more … A piano is pushed to the right across the room.

Balanced & Unbalanced forces Which diagram(s) show BALANCED forces?

Balanced Forces Forces acting on an object that are opposite in direction and equal in size Causes no change in velocity

Time for a DEMO! UNBALANCED forces cause a CHANGE IN VELOCITY (acceleration)!

Which object(s) will ACCELERATE?

Unbalanced Forces & Motion WS Time for a WS! Unbalanced Forces & Motion WS

The Big Misconception Read The Big Misconception Handout!

Anna is right!! These are BALANCED FORCES No ACCELERATION That means, NO CHANGE IN VELOCITY! It could be moving, but it will keep moving at a constant speed in the same direction. It could be at rest, but it will remain at rest.

Forces DO NOT CAUSE MOTION! FORCES CAUSE ACCELERATION!

NET FORCE Net Force = OVERALL FORCE Force is measured in Newtons (N). What is the NET FORCE on each object?

400 N 200 N 20 N

Force & Acceleration WS Got it? Time for a WS! Force & Acceleration WS

Newton’s First Law of Motion An object at rest will remain at rest and an object in motion will continue moving at a constant velocity unless acted upon by an unbalanced force. Things are LAZY…they keep doing what they’re already doing unless an UNBALANCED force causes a change!

The Law of Inertia Newton’s First Law of Motion “Law of Inertia” Laziness tendency of an object to resist any change in its motion increases as mass increases

In a nutshell…

Demo: Magic Golf Balls

Demo: Magic Coins

More examples…

How fast are you going when your face hits the pavement?

Time for a Lab! 1st Law of Motion Lab

Demo: Tossing a ball in a car (moving at a constant velocity). Where does it land?

Time for a WS! 1st Law of Motion WS

Newton’s Second Law of Motion Force = Mass x Acceleration F: (N) m: (kg) a: (m/s2) 1 N = 1 kg ·m/s2 F = ma m F a

Time for a WS! 2nd Law WS

Demo:

Time for a Lab! 2nd Law Lab

Demo:

Back to the BIG MISCONCEPTION! Why does it take an UNBALANCED force to cause an acceleration? Because F = m • a Fnet = 0 0 = m • a A = 0 It can’t accelerate!

Demo: How does a CONSTANT VELOCITY affect FORCE?

Newton’s Third Law of Motion When one object exerts a force on a second object, the second object exerts an equal but opposite force back on the first.

Demo:

Problem: How can a horse pull a cart if the cart is pulling back on the horse with an equal but opposite force? Aren’t these “balanced forces” resulting in no acceleration? NO!!!

Answer: forces are equal and opposite but act on different objects they are not “balanced forces” Balanced forces act on the SAME OBJECT

Demo:

Problem: A high-speed truck and a BUG have a head-on collision. The bug is crushed, while nothing happens to the truck. Do they hit each other with equal force?

Answer: Yes! Equal, but Opposite Forces! The force acting on the bug is enough to crush the bug. The same force acting on the truck isn’t enough to hurt the truck.

Time for a WS! 3rd Law WS

Identify the Action-Reaction Force Pairs

Identify 2 Action-Reaction Force Pairs

Identify 5 Action-Reaction Force Pairs

Time for a Lab! 3rd Law Lab

Do you understand? Time for a Review WS! May the NET FORCE be with you!