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Motion Chapter 11

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**What is physics? The study of matter and energy and…**

The interactions between the two… Through forces and motion Topics in physics Motion, forces, work, power, machines, energy, waves, heat, light, sound, optics, electricity, magnetism and more…

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Frame of Reference Motion of an object in relation to a fixed body or place. To describe motion accurately and completely THE MOST COMMON FRAME OF REFERENCE: The Earth

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**Relative Motion Is the movement in relation to a frame of reference**

Example: A train going past a platform (see movement) People riding the train feel no movement

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**Distance Length of a path between two points How far, long, wide, etc**

Metric units for distance – meter, kilometer, centimeter, etc. Units should match the distance – longer units for longer distances, shorter units for shorter distances

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**Measuring Displacement**

the direction from the starting point and the length of a straight line from the starting point to the ending point Involves distance and direction

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**Combining Displacement**

Vector—is a quantity that has magnitude and direction Add displacements using vector addition If vectors are in the same directions, add them Ex: 10 meters meters = meters If vectors are in the opposite direction, subtract them 20 meters meters = 5 meters Resultant vector—the vector sum of two or more vectors

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**Steps in solving word problems 1. READ the problem carefully. 2**

Steps in solving word problems 1. READ the problem carefully. 2. Choose the correct FORMULA and write it down. 3. Identify INFORMATION given in the problem. Determine the VARIABLE, what you are looking for 4. Substitute the known INFORMATION into the formula. 5. SOLVE the equation for the variable. 6. Give the answer including NUMBER and appropriate UNITS.

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**v Speed Rate of Motion: Change of position in a given amount of time.**

Formula: Speed = Distance/time Units: km/h, m/s v = speed v = average speed d = distance t = time d v = t v vvv Delta T diagram

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**Speed Average Speed Is computed for the entire duration of a trip**

Instantaneous Speed Is the rate at which an object is moving at a given moment of time Speed right now

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**Speed Practice Problems**

How long does it take a bird to fly 300km if it travels at a speed of 50 km/h?

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**2. Alex rode his bicycle 60 kilometers in 4 hours**

2. Alex rode his bicycle 60 kilometers in 4 hours. How fast was he going?

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**3. Joe can pitch a baseball 32 m/s and the ball crosses the plate in 1**

3. Joe can pitch a baseball 32 m/s and the ball crosses the plate in 1.5 seconds. How far away is the plate?

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**4. Kayla runs 90 meters with a speed of 15 m/s. How long did it take?**

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**Velocity Velocity= Speed in a given direction. Velocity is a vector**

You combine velocities the same way you combine displacement Same direction, add them Opposite direction, subtract them

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Velocity Formula V=Δd/Δt V=velocity d=distance t=time Units: m/s

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**Graphs of Speed and Velocity**

Constant Speed Not Moving Constant speed and then not moving

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**Acceleration Rate of change in velocity. Acceleration is a vector**

Formula: a = vf – vi or Δv t t Unit: m/s2 Variables need to solve acceleration problems 2 Velocities Time

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**Deceleration Negative Acceleration**

Solve it just like the acceleration problem but the answer is always NEGATIVE Tom sees a stop sign. He notices his speedometer is on 50 km/h, applies the brakes, and comes to a full stop in 10 seconds. What is his average acceleration in km/h/s? a = vf – vi or Δv t t a = ? vf = 0 km/h vi = 50 km/h t = 10 s a = 0 km/h – 50 km/h 10 s = -50 km/h = -5 km/h/s 10 s

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**Acceleration/ Deceleration Problems**

A car starts from rest and goes to 20 m/s in 4 seconds. What is the car’s acceleration?

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2. A runner starts to run and reaches a velocity of 100 m/s in 25 seconds? What is the car’s acceleration?

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**3. A train slows down from 200 m/s to a stop in 50 seconds**

3. A train slows down from 200 m/s to a stop in 50 seconds. What is the car’s deceleration?

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4. A train has an acceleration of 40 m/s2 during a period of 15 seconds. What is the train’s velocity?

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**Graphs of Acceleration**

Deceleration Constant Acceleration

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**Centripetal Forces Center Seeking**

Centripetal Force is a force that pulls an object towards the center. Center Seeking

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**Constant Speed and Circular Motion**

An object moving in a circular motion may have constant Speed even though it is accelerating. Why?

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**Answer: That object needs to change direction.**

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**3 ways objects accelerate**

Change in Speed only Change in Direction only Change in Speed and Direction

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