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Forces and the Laws of Motion

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- 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)

- 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

- 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

- Inertia: force that is resistant to the direction of the motion
- The forces are Unbalanced

- Examples: Inertia belts (seat belts)

- Concept: Acceleration
- The forces are unbalanced

- Examples: hitting a golf ball gently vs. hard.
- F = ma

Answer = _50__ newtons

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?

- 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: 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.

- Force that slows down falling objects due to the atmosphere and surface area of the object.

- Shows that objects are attracted to one another in proportion to their masses and their distances away from the object.

- 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