Forces and the Laws of Motion

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# Forces and the Laws of Motion - PowerPoint PPT Presentation

Forces and the Laws of Motion. Forces. Force is a push or pull on an object. Unit for force: N or Newton. Balanced forces Where there are two forces that counteract each other and result in no movement (EQUAL) Unbalanced forces One force is greater than the other force. (UNEQUAL).

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## PowerPoint Slideshow about ' Forces and the Laws of Motion' - clark-madden

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Presentation Transcript
Forces
• Force is a push or pull on an object.
• Unit for force:

N or Newton.

Balanced forces Where there are two forces that counteract each other and result in no movement (EQUAL)
• Unbalanced forces

One force is greater than the other force.

(UNEQUAL)

Friction
• A force that resists motion and can cause heat
• Lubricants help reduce friction
• Types of friction
• Sliding
• Rolling
• Fluid
• Static
Types of friction
• Static
• acts on objects that are not moving
• Always acts in opposite direction to applied force
• Sliding
• Opposes direction of motion as an object slides
• Less then static friction
• Rolling
• Friction that acts on rolling objects
• 100 to 1000 times less than static and sliding friction
• Fluid
• Opposes the motion of an object through a fluid
• Fluids include gases and liquids
• Air resistance – fluid friction acting on an object moving
• through the air
Newton’s Laws of Motion
• 1st Law: Objects at rest remain at rest, or objects in motion remain in motion unless acted upon by a force. (unbalanced)
• 2nd Law: The acceleration of a body depends on the ratio of the acting force to the mass of the body. (unbalanced)
• F = m x a
• 3rd Law: for every action there is an equal and opposite reaction. (balanced)
1st Law of Motion (Law of Inertia)
• Inertia: force that is resistant to the direction of the motion
• The forces are Unbalanced
• Examples: Inertia belts (seat belts)
2nd Law of Motion
• Concept: Acceleration
• The forces are unbalanced
• Examples: hitting a golf ball gently vs. hard.
• F = ma

Problem 1

How much force is needed to accelerate a

500.0 kg car at a rate of 4 000 m/s/s?

Problem 2

A 100 N force causes an object to accelerate at

2 m/s/s. What is the mass of the object?

Problem 3

A 1.5 kg ball is kicked with a force of 450 N.

What acceleration did the ball receive?

3rd Law of MotionAction/ Reaction
• Concept: Action/Reaction of objects
• Forces are balanced
• Examples: Stationary objects, rockets being launched

### Laws of motion Interactives

http://science.discovery.com/games-and-interactives/newtons-laws-of-motion-interactive.htm

Projectile

Motion

Motion of a falling object after being

given an initial forward velocity

Combination of initial vertical force

and downward force of gravity

Causes object to follow a curved path

Gravity and Free Falling Objects
• Gravity: The attraction between two objects.
• All objects fall at a rate of 9.8 m/s2
• Gravity acts betweentwo masses
• All masses exert the force of gravity – universal force
• Galileo did an experiment at the leaning tower of Pisa in Italy with bowling balls. Both balls fell at the same rate.
Air Resistance
• Force that slows down falling objects due to the atmosphere and surface area of the object.
Newton’s Law of Universal Gravitation
• Shows that objects are attracted to one another in proportion to their masses and their distances away from the object.
Feather vs. Rock
• Earth: feather would float down (air resistance) while the rock would drop at 9.8 m/s/s
• Moon: feather and rock would drop at same rate due to no atmosphere and air resistance.
• vac·u·um[ vákyooəm ]
• space empty of matter: a space completely empty of matter but not achievable in practice on Earth
• space with all gas removed: a space from which all air or gas has been extracted
• emptiness caused by absence: an emptiness caused by somebody or something's absence or removal
• Both fall at the same rate due to there being no air.
Gravity and Weight

Gravi

ty

Mass – measure of amount of inertia

Weight – force of gravity pulling on an object

Weight is product of mass and acceleration due to gravity ( 9.8 m/s/s)

W = mg

W- weight in newtons

m- mass in kilograms

g- acceleration due to gravity in meters per second squared