Unit 7 Section 3: Newton's First Law

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DO NOW: Write what you think the example words mean in your lab manual.

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Unit 7 Section 3: Newton's Laws

Multiple Choice

What is the formula for average speed?

• $$s=\frac{dis\tan ce}{time}$$  

• $$s=\text{time/distance}$$  

• $$s=dis\tan ce\ \times\ time$$  

• $$s=\ dis\tan ce\ +\ Time$$  

Fill in the Blanks

Pete is driving down 7th Street. He drives 150 meters in 18 seconds. Assuming he does not speed up or slow down, what is his speed in meters per second? Round to two Decimal Places

Multiple Choice

How is velocity different from speed?

• Speed is velocity in a given direction

• Velocity is speed in a given direction

• They are the same

• Velocity is how much speed changes in a given amount of time

Multiple Choice

A push or pull exerted on an object is called a(n):

• Force

• Net force

• Momentum

• Speed

Multiple Choice

What is the net force in this picture?

• 0 N

• 75 N

• 150 N

• 5625 N

Drag and Drop

The force that one surface exerts on another when the two rub against each other is called ​

Placeholder

Drag these tiles and drop them in the correct blank above

friction

acceleration

velocity

gravity

mass

Multiple Choice

Ted is trying to move a fridge through his house, he gets stuck on a carpet and even though he is pushing the fridge, it is not moving. What force is acting against him?

• gravity

• Static friction

• Sliding Friction

• normal force

Multiple Choice

Forces can be added together only if they are

• acting on the same object.

• balanced forces.

• unaffected by gravity

• substantial.

Multiple Choice

Review: Which of the following equations is the equation for Acceleration?

• $$a=\frac{V_f-V_i}{T}$$  

• $$a=V\cdot T$$  

• $$a=\frac{d}{t}$$  

• $$a=\frac{S\cdot V}{T}$$  

Multiple Choice

The law of universal gravitation states that any two objects in the universe that have mass, without exception,

• attract each other

• repel each other.

• combine to provide a balanced force.

• create friction.

Lesson Objectives

• Describe Newton's First Law of Motion

  • Understand Inertia and how it affects objects

• Describe Newton's 2nd Law of Motion

  • Calculate Acceleration when given a Force and a mass

• Describe Newton's 3rd Law of Motion

Newton's First Law of Motion

• Objects do not start or stop moving at random, but only in response to forces

• An object at rest will stay at rest until acted upon by a nonzero force, and

  an object in motion will remain in motion at a constant velocity until acted upon by a nonzero net force

Inertia

• In the 1500s Galileo proposed the concept of inertia

  • Inertia: the tendency of an object that shows they tend to remain how they are.

    • A property all objects have

• Every time something Moves or stops moving, it needs to overcome inertia

• Inertia is directly related to mass

  • The more mass something has, the harder it is to start or

    stop

    • You feel inertia when you are in a car that stops suddenly

Newton's First Law of Motion & Concussions

Multiple Select

Inertia refers to ___________

(select all the apply)

• the tendency of moving objects to remain in motion

• the force which keeps moving objects in motion with a constant velocity

• the force that keeps stationary objects at rest

• the tendency of stationary objects to remain at rest

Multiple Choice

All Objects have Inertia

• True

• False

Multiple Choice

The greater the mass of an object...

• the easier the object starts moving.

• the greater its inertia.

• the more balanced it is.

• the more space it takes up.

Recall: Acceleration

• Acceleration is the change in velocity over time

  • Involves changes in speed as well as changes in direction​

• Acceleration occurs in both horizontal movement as well as vertical movement

Mass and Acceleration are Related

• More massive Objects are more difficult to accelerate

  • Experiments show that doubling the mass of an object halves the acceleration, tripling thirds it, etc.

  • Acceleration and mass are inversely related​

Newton's Second Law of Motion

• ​When an Unbalanced Force is applied to a mass, it causes it to accelerate

  • The acceleration of an object is directly proportional to the net force on the object and is inversely proportional to the mass of the object

    • ​a = f/m

    • f=m*a​

Fill in the Blanks

If you apply a net force of 5 N on a cart with a mass of 5kg, what is the acceleration of the cart?

A Force is Part of an Interaction

• Force is not a trait of an object, it is something an object does

• Force is more than just a single push or a pull and is an interaction between two objects

  • Both the object exerting the force and the object receiving the force is part of the interaction

• Example: If a truck collides with a car, the truck exerts a force on the car and the car exerts a force on the truck at the same time

  • These forces are equal in strength and occur in opposite directions

Newton's 3rd Law: The Law of Action & Reaction

• Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first

  • To every action, there is an equal and opposite reaction

  • One force is the action force, and the other force is the reaction force

Multiple Choice

Think about it: When a heavy football player and a light one run into one another, does the light player exert as much force on the heavy player as the heavy player exerts on the light player?

• Yes

• No

• Sometimes

Multiple Choice

Think about it: Would the damage to the heavy player be the same as the damage to the lighter player

• Yes

• No

• Sometimes

Action & Reaction on Objects of Different Masses

• Recall Newton's Second Law: a= F/M

• Newton's Third law​ states that every action has an equal and opposite reaction, so why do objects respond differently?

  • Because they have Different Masses

  • A given Force Exerted on a small mass produces a large acceleration, while the same force exerted on a large mass produces a small acceleration

Action & Reaction on Objects of Different Masses

• ​If Forces are equal and Opposite, why don't they cancel out to zero?

  • Because they act on different bodies

    • When you kick a ball, an action force acts on the ball, the reaction force is on the foot​

Multiple Choice

When you push a marble with a 0.5 N force, what does the marble do?

• accelerate at 10 m/s²

• Resists being pushed

• Stay at rest

• Pushes on you with a 0.5 N Force

Multiple Choice

A karate chop delivers a force of 3000 N to a board that breaks. The force that the board exerts on the hand during this event is

• less than 3000 N

• 3000 N

• Greater than 3000 N

• Cannot tell from the given information

Multiple Choice

When you throw a basketball, your force on the ball accelerates it. The ball pushes back on you with an equal and opposite force. Why don't you accelerate as much as the ball?

• The reaction force is only on your hand, not the rest of you

• Friction stops you from acceleration

• Your acceleration is much smaller than the ball's because of your larger mass