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Force and motion Unit 3

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**Key Terms Motion- a change in position, measured by distance and time.**

When motion is changed it is called applied force. Force- an external agent that causes the motion to move by energy, usually in a push/pull manner. Speed- distance traveled by a moving object per unit of time (only gives distance and time) Speed = Distance/Time S=d/t

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**Velocity- rate (how fast) a change in position occurs**

Accounts for distance, time, and direction of travel. Acceleration- the increase of velocity (speed) and how it changes Vector- magnitude (how far) and direction (from point A to point B) Deceleration- the decrease in velocity (speed)

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**Acceleration Formula A = Vf - Vi/t**

f= Final Velocity - Starting Velocity divided by the time to change the velocity. i=Intial Velocity over time A = m/s2, V = m/s, t = s

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Isaac Newton An English physicist, mathematician, and astronomer Changed our view of the universe with his three laws of motion Inertia- tendency of an object resist changes in it’s state of motion.

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**1st Law of Motion-Law of Inertia**

An object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted on by an unbalanced force. A seatbelt strapped to a passenger in a moving car. A moving vehicle and a sitting cup of liquid.

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**2nd Law of Motion- Law of Dynamics**

This law is best explained with the equation: Force = Mass x Acceleration Acceleration is always in the direction of the unbalanced force. The units of force are Newtons. 1 Newton = 1 kg x 1 m/s/s (m/s2)

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**3rd Law of Motion- Law of Action/Reaction**

For every action, there is an equal and opposite reaction (forces always act in pairs).

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**Check your Understanding**

While driving down the road, a firefly strikes the windshield of a bus and makes a quite obvious mess in front of the face of the driver. This is a clear case of Newton's third law of motion. The firefly hit the bus and the bus hits the firefly. Which of the two forces is greater: the force on the firefly or the force on the bus? Which law is this? Answer: They have equal force, the mass of the bug is smaller therefore it cannot withstand the collision. Newton’s 3rd Law of Motion

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**Bell Work 9/22/10 1. What is the formula for speed?**

Solve the following problem using the formula for speed: In a track meet Chase threw a javeline 126m through the air. While in flight, the javeline traveled at an average speed of 9.0m/s. How long did the javeline remain in the air?

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More Vocab Free Fall - an object falling under the influence of gravity. Near the surface of the earth, all objects are accelerated by gravity at a rate of 9.8 m/s2. Friction - a force that opposes motion (important) Gravity- force of attraction between all objects Gravity is the weakest of the known natural forces, only becoming obvious when massive objects like planets and stars are involved

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**Recognizing Newton’s Laws**

Balanced Force- do not cause a change in motion, they are equal in size and opposite in direction. Unbalanced Force-causes motion and are not opposite or equal.

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**p = m • v Momentum- quantity of motion an object has**

p=momentum m=mass v=velocity Actions and Reactions: Equal magnitude and opposite direction i.e. club and a golfball p = m • v

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