Section 1: The Nature of Force

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# Section 1: The Nature of Force - PowerPoint PPT Presentation

Section 1: The Nature of Force. Force – a push or pull on an object; causes an object to accelerate. 3 m/s. 0 m/s. Calculating Force. Force = (mass)(acceleration) F = ma measured in units of: kilogram-meter/second squared (kgm/s 2 ). kilogram-meter/second squared a.k.a. Newton (N).

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### Section 1: The Nature of Force

Force – a push or pull on an object; causes an object to accelerate.

3 m/s

0 m/s

Calculating Force

Force = (mass)(acceleration)

F = ma

measured in units of:

kilogram-meter/second squared

(kgm/s2)

Two Types of Forces

balancedforces – forces of equal strength & acting in opposite directions; net force always equals zero Newtons.

5 N

5 N

Net force = 0 N

unbalancedforces – forces of unequal strength &/or act in different directions; causes an object to move.

2 N

5 N

Net force =

3 N

3 N

5 N

UnbalancedForces

8 N

3 N

~7 N

5 N

5 N

Section 2: Friction & Gravity

friction- the force that two surfaces exert on each other when they rub against each other.

4 Types of Friction: (strongest to weakest)

• Static
• Sliding
• Rolling
• Fluid

- air resistance is the most common form.

gravity – a force that pulls objects toward each other.

Gravity causes objects to accelerate toward earth at:

9.8 m/s2.

Law of Universal Gravitation

states that due to gravity every object in the universe is attracted to every other object in the universe.

Weight

weight is the gravitational pull on an object.

weight = (mass)(gravity)

w = mg

measured in units of:

Kgm/s2 a.k.a. Newtons

# of lbs / 2.2 = # of kgs.

w = (# of kgs.)(9.8 m/s2)

Gravity in the Solar System

Moon

1.2 m/s2

Venus

7.98 m/s2

Jupiter

31,000 m/s2

Sun

3,244,816.1 m/s2

Newton’s First Law(Law of Inertia)

An object at rest will remain at rest, and an object in motion will remain in motion at a constant velocity, unless an unbalanced force acts upon it.

Newton’s Second Law

force, mass and acceleration are related with the formula:

F = ma

50 N

6 m/s2

300 kg

12 m/s2

100 N

300 kg

6 m/s2

100 N

600 kg

Newton’s Third Law

if one object exerts a force on another object, then the second object will exert a force of equal strength in the opposite direction back on the first object.

Fuel

Gas

momentum – the product of an object’s mass and velocity.

momentum = (mass)(velocity)

p = mv

measured in units of:

kilogram-meter/second

Law of Conservation of Momentum

states that: the total momentum of a group of objects remains constant

in other words:

the total momentum of objects before a collision equals the total momentum after a collision.

Before the collision

8

C

0.3 kg

0.25 kg

1.5 m/s

0 m/s

p = (0.25 kg)(1.5 m/s)

p = (0.3 kg)(0 m/s)

p = 0 kgm/s

p = .38 kgm/s

pt =.38 kgm/s + 0 kgm/s

pt =0.38 kgm/s

After the collision

8

C

0.3 kg

0.25 kg

0.75 m/s

0.63 m/s

p = (0.25 kg)(0.75 m/s)

p = (0.3 kg)(0.63 m/s)

p = 0.19 kgm/s

p = 0.19 kgm/s

pt =0.19 kgm/s + 0.19 kgm/s

pt =0.38 kgm/s