Lesson 1.3

Lesson 1.3 : Newton's First and Second Laws, Forces

Newton's First Law (inertia)

• an object in motion stays in motion...

• an object at rest stays at rest...

• UNLESS it is acted on by an outside force

Force

• any influence that can change the motion of an object

• force is a vector: has both magnitude and direction

• multiple forces working at once: balanced or unbalanced

• units: Newtons (N)

Net Force

Overall direction and size of movement after all forces are considered

Free Body Diagram

Shows all of the forces acting on an object at once

Multiple Choice

Applied force is 10N to the right. Friction force is 7N to the left. What is the net force? (mag and direction)

• 3N left

• 3N right

• 17N left

• 17N right

Multiple Choice

3 books are sitting on the table: 5N, 10N, 15N

What is the gravitational force pulling on the books?

• 30N up

• 30N down

• 10N left

• 25N right

Multiple Choice

3 books are sitting on the table: 5N, 10N, 15N

What is the normal force on the books?

• 30N up

• 30N down

• 10N left

• 25N right

Multiple Choice

3 books are sitting on the table: 5N, 10N, 15N

If the normal force is 30N up, and the gravitational force is 30N down, what is the net force?

• 60N left

• 60N right

• 0N

• 30 N down

Newton's 2nd Law

Force = mass x acceleration

F=ma

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Acceleration = change in speed over time

Flat vs. Crinkled Paper Demo

Air resistance opposes gravity

How do you think parachutes work?

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Free body diagram practice​

Parachute Lab

​Lab Steps

• ​Design a parachute with your group

• ​Drop your parachute weight 3 times and record data

• ​Edit design and perform another 3 trials

• ​Compare and analyze data

Acceleration due to Gravity

• ​Gravity pulls objects toward earth, causing them to accelerate

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  ​The rate that objects fall due to gravity is the same for every object

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• They gain speed at the same rate when falling (unless acted on by other forces such as air resistance)