Laws of Motion Mrs Wolfe If I have

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? • 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?

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 20 N

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” • 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! • 1 st Law of Motion Lab

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

Time for a WS! • 1 st Law of Motion WS

Newton’s Second Law of Motion • Force = Mass x Acceleration F: (N) m: (kg) a: (m/s 2) 1 N = 1 kg ·m/s 2 F = ma F m a

Time for a WS! • 2 nd Law WS

Demo:

Time for a Lab! • 2 nd 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! • 3 rd Law WS

Identify the Action-Reaction Force Pairs

Identify 2 Action-Reaction Force Pairs

Identify 5 Action-Reaction Force Pairs

Time for a Lab! • 3 rd Law Lab

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