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Motion, Acceleration, and Forces Physical Science 2012-2013

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Motion Section 3-1 Motion is a change in position of an object

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Distance vs. Displacement

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Distance The total length of the path an object follows:

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Displacement The distance and direction of an objects final position from its initial position Displacement includes both a length/size and direction and is called a vector

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What is the actual displacement?

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Speed The distance an object travels per unit time. We use metric (SI) units and it is meters per second (m/s) Usually the speed of an object changes as it moves from one place to another

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Instantaneous Speed The speed of an object at a single point in time Speedometer

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Average Speed The total distance traveled divided by the total travel time ___ V = d/t ____ V = average speed d=distance t=time

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Practice Problems What is the average speed of a car that travels a distance of 750m in 25s ? What is the average speed of a motorcycle that travels a distance of 300m in 10s ? What is the average speed of an airplane traveling a distance of 1000m in 10s ?

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Velocity The speed of an object and the direction of the motion Objects have different velocities if they are moving in different directions or a different speeds

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Graphing Velocity Time vs. Distance Graph

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Acceleration Section 3-2 Acceleration is the change in velocity divided by the time it takes that change to occur Acceleration

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ChangingChanging Direction A change in velocity can be either a change in how fast something is moving or a change in the direction of the movement

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Calculating Acceleration When an object moves from one place to another, it might speed up, slow down, and change directions many times. Each change in velocity causes the acceleration of the object to change

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Acceleration Equation

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Calculation Positive Acceleration An airplane starts at rest and moves down the runway in a single direction. After accelerating for 20s it reaches a speed of 80m/s. What is the acceleration?

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Calculating Negative Acceleration A car is moving in a straight line at a constant sped of 3m/s and comes to a complete stop in 2s. What is the acceleration?

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Motion and Forces Section 3-3

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What is Force? Force is a push or pull that one object exerts on another Force can cause the motion of a object to change.

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Baseball, Tennis, and Billiards

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Balanced Forces Force does not always change velocity, two or more equal forces acting on an object in opposite directions can cancel each other out. The net force is zero.

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Unbalanced Forces Unequal forces applied in opposite directions lead to a net force in the direction of the larger force and movement in that direction

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Friction The force that opposes the sliding motion of two surfaces that are in contact

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What Causes Friction? Frictional force depends on the materials that the surfaces are made of and the roughness of the two surfaces All surfaces have bumps and dips in them that can cause contact and thereby friction (microwelds)

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Frictional Force FF increases when the force pushing the surfaces together increases.

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Static Friction The frictional force that prevents two surfaces in contact from sliding past each other. Once the applied force is greater, the object will move.

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Rolling Friction Rolling friction is usually much less that static friction, that is why we use wheels!

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Air Resistance This force opposes the motion of objects that move through the air. Air resistance acts in the opposite direction of the objects movement The greater the surface area of the object the greater the power of air resistance on that object

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More surface area means a slower fall

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Terminal Velocity As an object falls it accelerates due to gravity, however air resistance eventually steps in to slow the object to a speed that no longer increases…that equaled out speed is called terminal velocity!

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