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**Speed, Velocity, Acceleration**

BY: BRIANNA SHIELDS

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DO NOW- Get hmwk out! Complete the physics handout on front counter

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GOAL To interpret graphs and solve word problems involving speed, velocity, acceleration and momentum

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**Change in position during a time period 3 types of motion**

Speed Velocity Acceleration

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Speed 1. Definition: Rate at which an object moves 2. Formula: Distance divided by time (d/t) 3. Units: m/s or km/s

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Speed 4. Constant speed - speed that doesn’t change 5. Average speed- add speeds, divide by total number

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**Speed: Average vs. Instantaneous**

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**Speed 6. Graphs: Time: x-axis Distance: y-axis Constant speed**

Changing speed Copy samples of these into your notebook

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**Cheetah Speed Graph In one second how far had the cheetah run?**

In three seconds how far had the cheetah run? What was the cheetah’s average speed?

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**Bicycle Graph After one hour how far had she traveled? Two hours?**

Three hours? Four hours? Is she traveling at a constant speed? Why/why not During which hours was her speed the greatest? What does the flat line on the graph indicate?

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Distance vs. Time

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**Calculating Speed: Example**

If 2 runners ran the same distance (10km) but one completed it in 3600 seconds and the other in 2800 seconds, what were each of their average speeds? 1: d/t 10km/3600 sec km/sec 2: d/t 10 km/ 2800 sec km/sec Runner 2 has greatest average speed!

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**Calculating Speed: Example**

Spirit of Australia, a hydroplane boat, made speed records by traveling 239 miles in 0.75 hours (45 minutes). What is it’s record breaking speed? d/t miles/ 0.75 hr

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Velocity 1. Definition: Describes speed plus direction (n, s, e, w) 2. Formula: D/T plus direction 3. Units: m/s or km/s, north, south, east or west

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**4. Velocities can be combined**

Velocity 4. Velocities can be combined Add velocities when in same direction Velocities in opposite direction= subtract

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**Velocity 5. Graphs: Time: x-axis Distance: y-axis**

(same as speed graphs but also has direction)

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**Calculating Velocity: Example**

If a runner is running east at 10 m/s sec, what is her velocity? 10 m/s east

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**Calculating Velocity: Example**

If you’re rowing a boat downstream at 16 km/hr, and the curren is moving at 10 km/hr. How fast does the boat “look” like it’s going to someone on shore? (Draw a picture too!) 26 km/hr downstream

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**Calculating Velocity: Example**

If you’re rowing a boat upstream at 15 km/hr, against a current moving at 8 km/hr. What is you’re actual velocity to an observer on the shore? 15-8 7 km/hr upstream

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**Calculating Velocity: Example**

If you are running up an escalator at 2 steps per second and its moving downward at 3 steps per second, what is the total velocity? In what way are you moving? 3-2 -1 (you are actually moving backwards, down the escalator, although you’re running up it)

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**1. Definition: Rate of change in velocity**

Acceleration 1. Definition: Rate of change in velocity Speeding up, slowing down, changing direction 2. Formula: Final velocity minus original velocity, divided by time 3. Units: m/s/s or km/s/s

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Acceleration 4. Increasing velocity - positive acceleration 5. Decreasing velocity - negative acceleration- deceleration

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**Acceleration 6. Graphs X- axis- time Y-axis- distance**

Object must be changing velocity Line, is smooth and curved (not straight)- “changing line”

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**Acceleration Graph- Race Car**

1. From 0-1 sec how far did the race car go? 2. From 1-2 sec? 3. From 2-3 sec? 4. Is the car accelerating or decelerating? Explain.

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Velocity vs. Time

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**Comparing velocity and acceleration**

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**Calculating Acceleration: Example**

A roller coaster’s velocity at the top of a hill is 10m/s. Two sec later it reaches the bottom of the hill with a velocity of 26 m/s. What is the acceleration of the roller coaster? Vf-Vo T 26-10 2 8 m/s/s

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**Calculating Acceleration: Example**

A roller coaster’s velocity at the bottom of a hill is 25 m/s. Three seconds later it reaches the top of the next hill, moving at 10 m/s. What is the deceleration of the roller coaster? A = Vf-Vo T A = = m/s/s 2

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**Calculating Acceleration: Example**

A car is traveling at 60 km/hr. It accelerates to 85 km/hr in 5 seconds. What is the acceleration of the car? A = Vf-Vo T A = = 5.0 m/s/s 5

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**1. Definition: Depends on object’s mass and velocity**

Momentum 1. Definition: Depends on object’s mass and velocity Related to force upon impact 2. Formula: Mass x velocity 3. Units: Kg.m/s

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Momentum

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Momentum

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Momentum

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**Calculating Momentum: Examples**

If 2 football players are running at the same velocity towards an opponent. Player 1 weighed 170 lbs, player 2 weighed 250 lbs. Who is going to move the opponent farther? Why? Since both players were traveling at the same velocity, the larger player will have more momentum, thus, moving the opponent farther

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**Calculating Momentum: Examples**

Why would it be harder to stop a car traveling at 65 miles/ hr than it is to stop one traveling at 35 miles/hr? Explain If they have approximately the same mass, the faster car will gather more momentum, according to the equation: momentum = mass x velocity

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**Calculating Momentum: Examples**

What is the momentum of a 0.3 kg bluejay running into a window while flying at 17 m/s? momentum = mass x velocity = 0.3 x 17 = 5.1 kg m/s

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Websites Fear of Physics

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**Assignment Write the homework assignment into your agenda:**

Practicing Motion

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