Sir Isaac Newton

Legend

Newton made a connection between why objects fall to the earth and what keeps the objects moving when he watched an apple fall– Unbalanced force caused the apple to fall

down on earth– Unbalanced force on the moon kept the moon

moving in a circular motion– Force of attraction--gravity

Review Force

• What is force?– A force is a push or a pull.

Video Time

St. Mary’s Physics: First Law

Sir Isaac Newton

– 1st Law – an object at rest or in motion stays at rest or

in motion unless acted upon by an outside force

* Known as the “Principle of Inertia”– 2nd Law – describes how an object accelerates or

changes direction when a force is applied to it

* F = ma– 3rd Law – for action there is an equal and opposite

reaction

Newton’s 1st Law of Motion

• An object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force. (outside force)

The velocity of an object remains constant unless acted on by an unbalanced force.

““Law of Inertia”Law of Inertia”

Newton’s 1st Law of Motion

Newton’s 1st Law of Motion

• Inertia - the resistance an object has to a change in its state of motion. [Newton’s 1st Law]

• Equilibrium - if the net force on an object is zero, then it is said to be in equilibrium.– An object is in equilibrium when: at rest or

moving at constant velocity.

Examples of equilibrium

• Equilibrium - resultant = 0 N

• Example 1

 

                                                                                                                                                                    

Examples of Equilibrium

• Velocity is Constant

• (rest or constant v)

 

Wacky Pennies

• What is Newton’s First Law?

• Purpose: Does the mass of an object effect the inertia.

 

Wacky Pennies

• Procedures:– 1. Stack 4 pennies on your table.– 2. Aim one penny at the bottom of the stack of 4 and

flick with your finger.

– 3. Make observations on a separate sheet of paper.– 4. Flick a stack of 2 pennies in a stack of 4 pennies.– 5. Make observations on a separate sheet of paper.– 6. Flick a stack of 4 pennies in a stack of 4 pennies.– 7. Make observations on a separate sheet of paper.

Wacky Penny Analysis

• 1. Explain your observations in terms of Newton’s 1st Law.

• 2. Does the mass of an object effect the inertia? Explain?

Wacky Pennies

• Mass is the measure of inertia and if you change the mass the inertia will change

Balancing Act

• Purpose: To remove a card from underneath a penny and keep the penny balanced.

Balancing Act

• 1. Balance a card (index/playing) on your index finger.

• 2. Place a penny on top of the card over your finger and balance the two together.

• 3. Squarely hit/flick the side of the card with your other index finger. If you properly hit the card, where does the coin end up?

• Please fill in the following chart with your observations, either at rest or moving:

•  

Object State of Motion

At Rest/Moving

Before it was hit

During it being hit

After it was hit

Card

Coin

Balancing Act Analysis

• 1. When does the object move?

• 2. How does this activity relate to the “pull the tablecloth” trick used by magicians?

2nd law of motion

• The acceleration of an object depends on the mass of the object and the amount of force applied

Newton’s Second law of Motion

• Acceleration decreases if mass increases

• Acceleration increases if mass decreases

• Acceleration increases if force increases

• Acceleration decreases if force decreases

FORMULA

F = M X A

Practice

• What is the force being applied to the car?

Other formulas to use

• A = F/M

• M = F/A

2nd law of motion

• http://www.teachertube.com/viewVideo.php?video_id=21643&title=Newtons_Law_2_on_FMA

Video Link Above

Newton’s 3rd Law

• Action-Reaction: for every action there is an opposite and equal reaction.

Momentum

The product of the mass and velocity of an object

Formula:

p= m x v

p= momentumm= massv= velocity

Units: kg x m/s (in a direction)

Conservation of Momentum

• Any time any objects collide, the total amount of momentum stays the same. – Example: Cue ball and billiard ball:

• Once you hit the cue ball it has a certain amount of momentum.

• It then hits the billiard ball• All of the momentum is transferred to the billiard

ball.• Therefore, the total amount of momentum stays

the same (opposite and equal reaction)

Finding Momentum

• An 85kg man is jogging with a velocity of 2.6 m/s to the North. Nearby, a 65kg man is skateboarding and is traveling with a velocity of 3 m/s North. Which person has a greater momentum? SHOW YOUR WORK!

• What is the momentum of an ostrich with a mass of 120kg that runs with a velocity of 16m/s north? SHOW YOUR WORK!