Aim: What are Newton’s 1 st and 3 rd Laws of Motion?

Aim: What are Newton’s 1st and 3rd Laws of Motion? Do Now: What is the weight of the box? m = 20 kg Fg = mg Fg = (20 kg)(9.8 m/s2) Fg = 196 N

So why isn’t the box accelerating downward? No acceleration means no unbalanced forces In other words: Forces are balanced FNet = 0 The table is pushing up with an equal force This is called the Normal Force (FN) FN = 196 N Fg = 196 N

Normal Force • Represented by FN • Supporting force from the surface the object is on • Perpendicular and away from the surface • If object is at rest in that direction, FN is equal to the objects weight FN Fg

Newton’s 1st Law of Motion Law of Inertia If all the forces acting on an object are balanced (FNet = 0): a. an object at rest remains at rest Penny in beaker Demo

b. an object in motion will remain in motion with a constant velocity

Inertia – the ability of an object to resist a change in motion • Objects at rest want to remain that way • Objects in motion want to remain that way • Inertia is dependent only on mass • (the more mass, the more inertia)

A boy is pulling a 30 kg sled with a force of 100 N at a constant velocity Draw a free – body diagram to illustrate this FN = 294 N FF = 100 N F = 100 N Are we missing any forces? Forces must be balanced Fg = 294 N Force of friction (Ff) – opposes the direction of motion

Object is at rest. What are the values of Forces A and B? Force A = 20 N Force B = 5 N 5 N 20 N

Newton’s 3rd Law – Law of Action – Reaction For every action there exists an equal but opposite reaction Demo – Balloon What is the action? What is the reaction?

Reaction – floor pushes on jumper Action – Jumper pushes on floor

Reaction – Floor pushes forward on foot Action – Foot pushes backward on floor

Reaction – Person pushes boat backwards Action – Boat pushes person forward

Reaction – Air pushes the rocket up Action – Rocket pushes the air down

Aim: What are Newton’s 1 st and 3 rd Laws of Motion?