DO NOW- Get hmwk out! Complete the physics handout on front counter
GOAL To interpret graphs and solve word problems involving speed, velocity, acceleration and momentum
Motion Change in position during a time period 3 types of motion –Speed –Velocity –Acceleration
Speed 1. Definition: Rate at which an object moves 2. Formula: Distance divided by time (d/t) 3. Units: m/s or km/s
Speed 4. Constant speed - speed that doesn’t change 5. Average speed- add speeds, divide by total number
Speed 6. Graphs: –Time: x-axis –Distance: y-axis –Constant speed –Changing speed Copy samples of these into your notebook
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?
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?
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!
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 239 miles/ 0.75 hr
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
Velocity 4. Velocities can be combined –Add velocities when in same direction –Velocities in opposite direction= subtract
Velocity 5. Graphs: –Time: x-axis –Distance: y-axis –(same as speed graphs but also has direction)
Calculating Velocity: Example If a runner is running east at 10 m/s sec, what is her velocity? 10 m/s east
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
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
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)
Accelerati on 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
Accelerati on 6. Graphs –X- axis- time –Y-axis- distance –Object must be changing velocity –Line, is smooth and curved (not straight)- “changing line”
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.
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 m/s/s
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 = = -7.5 m/s/s 2
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
Momentu m 1. Definition: Depends on object’s mass and velocity –Related to force upon impact 2. Formula: Mass x velocity 3. Units: Kg.m/s
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
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
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
Websites Fear of Physics Fear of Physics
Assignment Write the homework assignment into your agenda: –Practicing Motion