What we did in class today: Tuesday January 10th, 2012

• Note cards• Newton’s Laws Experiment• If absent make-up note cards

Force is a push or a pull.

Example: Forces are used to pick up a backpack, closea car door, or move a pencil across the desk top.

Mass is a measure of how much matter anobject contains.

Example: A basketball has more mass than abaseball.

Work is done on an object when the object moves in the same direction in which theforce is exerted.

Power is the rate at which you do work.Example: A cook increases his power when he beats eggs rapidly instead of stirring slowly. To calculate power, divide the amount of work by the time it takes to do the work.

Speed

Speed is how fast something moves or the distance it moves in a given amount of time.

To calculate speed you need to know both distance and time measurements. s = d/t (m/s)

Average speed is calculated by dividing total distance by total time.

Example : A middle school runner has the following times for the fourlaps of a 1600-meter race: 83 seconds, 81 seconds, 79 seconds, and77 seconds. The total time is 320 seconds and the total distance is1600 meters. The average speed is 1600 meters divided by 320seconds or 5 meters per second.

Instantaneous speed is the speed at which you arecurrently traveling at the moment.

Example: If you are driving along and look down at thespeedometer, your instantaneous speed would bedisplayed on your speedometer.

Velocity is a speed in a specific direction.

Example: If you say you are walking east at the speed ofthree meters per second, you are describing velocity.

Acceleration

Acceleration is a measure of how quickly the velocity is changing. If velocity does not change, there is no acceleration. ( m/s 2 ) a = v final – v initial t

Positive acceleration occurs when the accelerationis in the same direction as the object is moving andthe speed of the object increases.

Example: The car speeds up.

Negative acceleration occurs when the accelerationis opposite to the motion and the speed of the objectdecreases.

Example: The car slows down.

Newton’s Laws of Motion

Newton’s First Law states objects at rest remain atrest, and objects in motion remain in motion with samevelocity, unless acted upon by an unbalanced force.

INERTIA

Newton’s Second Law states the acceleration of an object depends on the mass of the object and the amount of force applied.

The acceleration of an object increases with increased force and decreases with increased mass.

F= mass x acceleration A= force/mass

Newton’s 2nd Law

Newton’s Third Law states when one object exerts aforce on another object, the second object exerts anequal and opposite force on the first object.

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