# Motion and Newton’s first law What is a force? Identifying forces Newton’s second law - PowerPoint PPT Presentation

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Chapter 4 Forces and Newton’s Laws of Motion. Motion and Newton’s first law What is a force? Identifying forces Newton’s second law Free-body diagrams Newton’s third law. Topics:. Sample question:.

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Motion and Newton’s first law What is a force? Identifying forces Newton’s second law

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Chapter 4

Forces and Newton’s Laws of Motion

• Motion and Newton’s first law

• What is a force?

• Identifying forces

• Newton’s second law

• Free-body diagrams

• Newton’s third law

Topics:

Sample question:

These ice boats sail across the ice at great speeds. What gets the boats moving in the first place? What keeps them from going even faster?

Slide 4-1

4.An action/reaction pair of forces

A.point in the same direction.

B.act on the same object.

C.are always long-range forces.

D.act on two different objects.

Slide 4-6

4.An action/reaction pair of forces

D.act on two different objects.

Slide 4-7

... is a push or pull.

... acts on an object.

... requires an agent.

... is a contact force or a long-range force.

... is a vector.

What Is a Force?

A force...

Slide 4-10

Galileo (1564-1642)

Developed the idea of experimental science

Re-examined natural motion of objects and how objects move

Made astronomical observations that challenged Earth-centered solar system model.

Newton (1642-1727)

Newton's work based on experiments of how objects interact.

His laws of motion and law of gravity described how all objects interact with eachother.

Newton’s Zeroeth Law of Motion

Objects are dumb - They have no memory of the past and cannot predict the future. Objects only know what acts directly on them in a given moment.

Slide 2-34

Newton's Zeroeth Law of Motion

DEMO - Pushing the cart on track

Identifying Forces:Freebody (Force) Diagrams and System Schema

Slide 2-34

Free-Body Diagrams

Slide 4-24

System Schema

• Draw a diagram where you write down the name of each object in the system and then draw a solid circle drawn around it. Draw two sided arrows like this between the object circles of objects that interact (This illustrates all interactions between the objects in this diagram). Draw an additional dotted line around the block to indicate it is the object of interest. This diagram is called a system schema.

• A system schema illustrates all the relevant interactions between the objects in a given physical situation

Newton's First Law of Motion

Every object continues in a state of rest or a state of motion with a constant speed in a straight line unless acted on by an unbalanced force.

Newton's First Law of Motion

DEMO - Air Puck motion

DEMO - Smash the HAND

DEMO - Tablecloth

What Causes Motion?

In the absence of any forces acting on it, an object will continue moving forever. Motion needs no “cause.”

Slide 4-8

Newton’s Second Law

Slide 4-22

Normal Force

Slide 4-15