Physics Motion Chapter 11 Frame of Reference Objects

Physics ~ Motion Chapter 11

Frame of Reference Objects are moving n How they are moving depends on your Frame of Reference n Comparison to other objects n Ex. Your body compared to the car n Ex. A fly inside the car (cheeseburger on dash) n Ex. Your body compared to Earth n (1800 km/h) sitting still – How can you speed it up? n

Choose your measuring stick Height n Walking distance n Car’s movement n Fly’s movement n Earth’s movement n Your movement inside the car when it is stopped n Make sure you use appropriate measurement for the most accurate measurement n

Stand Up… Take a piece of paper & pencil with you n Find a square on the floor to stand where nothing is in front of you for at least 7 squares. n Then follow the directions as they are read aloud to you n 1. Put something in your square to mark where you started n

2. Move 7 squares forward n 3. Write down how far you have traveled n 4. Move backward 4 squares n 5. Write down how far you have traveled n 6. Write down how far away you are from your beginning square n 7. Move backward 3 more squares n 8. Write down how far you have traveled n 9. Write down how far away you are from your beginning square n You should be back at the beginning n

Distance vs. Displacement n Distance – how far an object has traveled n Displacement – how far an object is from its beginning point

Need 10 yds to get the first down… n What happens when the quarterback gets sacked behind the line of scrimmage? n What does the team do if they’re on 4 th down and 18 yds to the first down line? n n PUNT the ball

Displacement vs. Distance What is your distance traveled from home now? n What is your displacement from home now? n Your distance traveled from home when your return this evening? n Your displacement from home when your return this evening? n

Figure it out…draw it out If I left home this morning and drove 3 blocks north, turned east & drove 3 blocks, then turned south & drove 3 blocks… n What is my distance? n Displacement? n You just drew vectors n How could I have made the trip shorter? n What would my distance be then? n My displacement? n

Speed SI unit = m/s n Speed = distance time n Average Speed = Total Distance n Total Time n n v=d t

Instantaneous speed Speed in that instant n Where do we find a meter for instantaneous speed? n Car n

The Race for Rose Speedway n Make a table like this: RACER DISTANCE METHOD TIME HOW FAST

Copy these steps for lab 1. Get a meter stick, 2 pieces of masking tape (or chalk), & stopwatch n 2. Measure a distance of 10 m (mark both ends with a piece of masking tape or chalk) n 3. Decide on 5 different ways you can travel 10 m n 4. Complete your race (make sure you fill in your data table as you go) n

Questions to answer on your lab paper 1. Which “race” method was the fastest? n 2. How do you know? n 3. Calculate how fast each “race” was n 4. What is the unit of measure for “how fast? ” n 5. Does it matter if the same person ran each race? n 6. Make a line graph of your race methods (use the x-axis as time) n

Distance Time Graph What you set up for your Race lab n What do the lines on your graph represent? n The Slope of your line represents speed n What if you marked your location every second and you had stopped at the 5 m mark for a few seconds…what would the line look like? n

It’s all relative… Car is sitting still at a stoplight n How fast is it moving? n Relative to the road? n 0 km/hr n Relative to the Earth? n 1800 km/hr n If the car was moving and the speedometer showed 80 km/hr…. … How fast is the car moving relative to the Earth? n

Velocity - It’s a vector Vector = a straight line segment whose length is magnitude and whose orientation in space is direction n Combine (add) vectors when more than one velocity is involved (p. 337) n SI unit is m/s n

Changing Velocity = Acceleration is the rate at which velocity changes n Acceleration is a vector too n SI unit is m/s 2 n Free fall on Earth = 9. 8 m/s 2 n When direction changes, there is acceleration even if the speed doesn’t change n Remember: Velocity = speed & direction n

Acceleration n Acc = change in velocity total time a = (vf – vi ) t

Figure it out… Car traveling at 10 m/s starts to decelerate steadily. Comes to a complete stop in 20 seconds. n What is its acceleration? n - 0. 5 m/s 2 n Airplane travels down a runway for 4. 0 sec. with an acceleration of 9. 0 m/s 2. What is its change in velocity? n 36 m/s n

Worksheet for you! n Yes, this will be on your EOC! n

Distance Time Graph What you set up for your Take a Walk lab n What do the lines on your graph represent? n The Slope of your line represents speed n What if you marked your location every second and you had stopped at the 10 m mark for a few seconds…what would the line look like? n