Unit 7 Section 3: Newton's First Law

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Unit 7 Section 3: Newton's Laws

Multiple Choice

What is the formula for average speed?

• $$s=\frac{dis\tan ce}{time}$$  

• $$s=\text{time/distance}$$  

• $$s=dis\tan ce\ \times\ time$$  

• $$s=\ dis\tan ce\ +\ Time$$  

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​

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