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Section 2.1Newtons First Law of Motion

Newton: Great Scientist or 80s Rock Star?English Physicist /Mathematician1642-1727Invented Calculus to explain what he observedDiscovered 3 LAWS OF MOTION

Use the Force, Lukebut only if you know what it is!A force is a push or pull, or any action that has the ability to change motion.Where is the force in these examples?

ActionWhat caused the force?Person lifts a boxPerson pulls object off the groundGun fires bulletExplosion pushes bulletBranch falls from treeGravity pulls branch to ground

Nothing can start or stop moving unless a force is applied!

O RLY?!?

YEAH RLY!

?Question?Can there be a change in the motion of anything without a force being applied?

NO!

Okay smarty, I think you got it!

Newtons First LawAn object at rest will stay at rest and an object in motion will continue in motion with the same speed and direction UNLESS acted on by a force.

?Question?So a space ship is going 75,000 m/s(or 75 km/s). It takes a left turn at Pluto, but never changes speed. Was there a force acting on it??

Yes!

In order to change direction,A force must be applied!

Which would you rather do?

Lift (move) a bag with groceries in it

Lift (move) a semi-truck

Easy choice, rightIt is much easier to lift the groceries and possibly impossible (for you weaklings, anyway) to lift the truck.

Why is one harder to move than the other?

MassYou remember massits the measure of how much matter an object has.

It turns out, the more mass something has, the more force is required to move it.Duh!

InertiaInertia is the property of objects to resist changes in motion.

If something is stationary, it resists attempts to move it

If something is moving, it resists attempts to slow it down (or speed it up)

The more mass something has, the more inertia it has, and this means that more force is required to increase or decrease its speed.

Which would you rather do?Part 2

Stop a bag of groceries that was thrown at you

Stop a semi-truck driving toward you

Put these in order:Least to greatest inertiaBaseball bat (900g)Bowling ball (7.2kg)Pencil (2.6g)Person (100kg)Paper (0.1g)

The greater an objects inertia, the greater theforce needed to change its motion

Newtons first law is often referred to as the law of inertia

Units of ForceSI unit of mass is kilogram (kg)SI unit of force is the NEWTON (N)

1 N of force can accelerate a 1kg object by 1 m/s

4.448 N = 1 lb(yes, weight is a measure of force)

What if there are multiple forces acting on an object?

Multiple Forces Add (like in math)If two or more forces are acting on an object in the same direction, the net (overall) force is the sum of all the forces

Opposite forces subtract

What is the net force on the ball?Which way is it going to move (if at all)?

2.1 Section Review1. State Newtons first law in your own words.

2. How is mass related to inertia?

3. What is the net force and how is it determined?

Important VocabularyForceNewtons first lawNewtonNet force