P H Y S I C S Chapter 3: Newtonâ€™s Laws of Motion Section 3A: Forces and Free-Body Diagrams

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P H Y S I C S Chapter 3: Newtonâ€™s Laws of Motion Section 3A: Forces and Free-Body Diagrams. Force. Action that changes an objectâ€™s state of motion Slow down Speed up acceleration Change direction. Two Types. 1) Contact Force: through contact push/pull

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P H Y S I C S

Chapter 3: Newton’s Laws of Motion

Section 3A: Forces and Free-Body Diagrams

Force
• Action that changes an object’s state of motion
• Slow down
• Speed up acceleration
• Change direction
Two Types

1) Contact Force:through contact

• push/pull

2) Field Force:at a distance

• gravity/electromagnetism
Free Body Diagram
• Shows all forces (vector) acting on an object
• Unit for force = N (Newton)

FN = 500 N

Fp= 1000 N

Ff = 200 N

Fg = 500 N

Newton
• The amount of force it takes to accelerate a 1kg mass at 1 m/s2
• 1N = 1kg*m/s2
Common Forces
• Fg = weight  downward
• FN = normal  perpendicular to surface
• Ff = friction (includes air)  opposite to motion
• Fp= push/pull
• FT= tension in string

FRICTION

FN

FRICTION

Fg

Net Force
• Vector sum of all forces on an object

ΣF = (summation) net force

• x and y components:

F(x) = F·cosθ

F(y)= F·sinθ

Fp(y)

Fp

θ

Fp(x)

In-Class Problem #1

A 9 N book sits at rest on a table.

ΣF = 0 N

In-Class Problem #2

A sky diver that weighs 600 N falls towards the earth and experiences a wind resistance of 250 N.

ΣF = 350 N 