Newton's Laws of Motion

Newton’s Laws of
Motion

Leaf Video

RULES

●Ask as many questions as you can

●Do not stop to discuss, judge or answer the questions

●Write down every question exactly as it is stated

●Change any statement into a question

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Categorize Your Questions

Open Ended Questions

Closed Ended Questions

Categorize Your Questions

Open Ended Questions

Require an explanation and cannot
be answered with “yes” or “no” or
with only one word.

Closed Ended Questions

Categorize Your Questions

Open Ended Questions

Require an explanation and cannot
be answered with “yes” or “no” or
with only one word.

Closed Ended Questions

Can be answered with “yes” or “no”
or with only one word

Categorize Your Questions

Open Ended Questions

Require an explanation and cannot
be answered with “yes” or “no” or
with only one word.

Closed Ended Questions

Can be answered with “yes” or “no”
or with only one word

Review your list of questions. Mark the open-ended questions with an O and
the closed ended questions with a C.

Name advantages and disadvantages of asking closed ended questions.

Name advantages and disadvantages of asking open ended questions.

Change one closed-ended question into an open-ended, and change one
open-ended question into a closed ended one.

Prioritize Your Questions

Choose the three most important questions from you list.

What was your reason for selecting those three?

Write these three questions on a new sheet of paper.

Galileo’s Concept of Inertia

Galileo’s Discovery

●Objects of different weight fall to the ground at the same time in the
absence of air resistance

●Demonstration: Paper and Textbook

Bowling Ball and Feather

Galileo’s Concept of Inertia

Force

●is a push or a pull

Inertia

●is a property of matter to resist changes in motion

●depends on the amount of matter in an object (its mass)

Galileo’s Concept of Inertia

●Balls rolling on downward-sloping planes pick up speed.

●Balls rolling on upward-sloping planes lose speed.

●So a ball on flat ground maintains its speed indefinitely.

●If the ball comes to rest, it is due to friction.

Mass

A measure of the inertia of a material object

Greater Inertia = Greater Mass

Unit of Measurement is the kilogram (kg)

Multiple Choice

The use of inclined planes for Galileo's experiment helped him to

• eliminate the acceleration of free fall

• discover the concept of energy

• discover the property called inertia

• discover the concept of momentum

Newton’s First Law of Motion

An object at rest stays at rest unless acted upon by an unbalanced force

An object in motion remains in motion unless acted upon by an unbalanced
force

What happened?

Net Force

Vector Quantity

●A quantity whose description requires both magnitude (how much) and
direction (which way)

●Can be expressed by arrows drawn to scale, called vectors

○Length of arrow represents magnitude and arrowhead shows direction

○Examples: force, velocity, acceleration

Vector

​https://www.youtube.com/watch?v=A05n32Bl0aY

Net Force

Net force is the combination of all forces that act on an object.

Example: Two 5-N pulls in the same direction produce a 10-N pull (net force of 10 N).

If the pair of 5-N pulls are in opposite directions, the net force is zero.

Multiple Choice

A cart is pulled to the right with a force of 15 N while being pulled to the left with a force of 20 N. The net force on the cart is

• 5 N to the left

• 5 N to the right

• 25 N to the left

• 25 N to the right

Multiple Choice

What is the net force acting on the box?

• 15 N to the left

• 15 N to the right

• 5 N to the left

• 5 N to the right

Support Force

●Support force (normal force) is an upward force on
an object that is opposite to the force of gravity.

●Example: a book on a table compresses atoms in the
table, and the compressed atoms produce the
support force.

Understanding Support Force

●When you push down on a
spring, the spring pushes back
up on you.

●Similarly, when a book pushes
down on a table, the table
pushes back up on the book.

Multiple Choice

When you stand on two bathroom scales with one foot on each scale and with your weight evenly distributed, each scale will read

• Your weight

• Half your weight

• zero

• More than your weight

Equilibrium of Moving Things

Equilibrium: a state of no change with no net force acting on the system.

Static Equilibrium

Example: A crate at rest (no change
in motion)

Dynamic Equilibrium

Example: A crate pushed at a stated
speed (no change in motion)

Multiple Choice

A bowling ball is in equilibrium when it

• is at rest

• moves in a straight-line path

• both of the above

• none of the above

Multiple Choice

You push a crate at a steady speed in a straight line. If the force of friction is 75 N, how much force must you apply?

• More than 75 N

• Less than 75 N

• Equal to 75 N

• not enough information

The Force of Friction

●Depends on the kinds of material and how much they are pressed
together

●Is due to tiny surface bumps and to “stickiness” of the atoms on a
material’s surface.

Example: Friction between a crate on a smooth wooden floor is less than that
on a rough floor.

Multiple Choice

The force of friction can occur

• with sliding objects

• in air

• in water

• all of the above

Multiple Choice

When Sanjay pushes a refrigerator across a kitchen floor at a constant speed, the force friction between the refrigerator and the floor is

• less than Sanjay's push

• equal to Sanjay's push

• equal and opposite to Sanjay's push

• more than Sanjay's push

Multiple Choice

When Sanjay pushes a refrigerator across a kitchen floor at an increasing speed, the force friction between the refrigerator and the floor is

• less than Sanjay's push

• equal to Sanjay's push

• equal and opposite to Sanjay's push

• more than Sanjay's push

Newton’s Second Law of Motion

Newton’s Second Law (the law of acceleration) relates acceleration and force.

Acceleration is directly proportional to net force.

To increase the acceleration of an object, increase the net force acting on it.

Newton’s Second Law of Motion

Newton’s Third Law of Motion

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

Multiple Choice

A soccer player kicks a ball with 1500 N of force. The ball exerts a reaction force against the player’s foot of

• somewhat less than 1500N

• 1500N

• somewhat more than 1500N

• none of the above

Newton’s Third Law of Motion

Action and Reaction Forces

●One force is called the action force; the other force is called the reaction
force

●Neither force exists without the other

●Are equal in strength and opposite in direction

●Always act on different objects

Multiple Choice

When you step off a curb, Earth pulls you downward. The reaction to this force is

• A slight air resistance

• nonexistent in this case

• you pulling the Earth up

• none of the above