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)

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 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?

3rd Law of Motion Action/ 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

Motion of a falling object after being 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 between two 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.

Both fall at the same rate due to there being no air. What about a vacuum? vac·u·um [ vákyoo əm ] 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