1 Dimensional Motion Conceptual Physics Position and Displacement

1 Dimensional Motion Conceptual Physics

Position and Displacement Position: Location of an object of interest at some given time (t). - Variable: Given by “x” and/or “y” Displacement: Change in position of an object of interest. - Variable: Given by Δx = xf - xi

Speed Average Speed: How far you travel in a certain amount of time. Not necessarily traveling at a constant speed. - Variable: |v|avg = distance / time or d/Δt – Unit of speed: m/s - Odometer and a stopwatch to measure. - Think of a road trip, your speed varies but on average you travel 75 on I 25. Instantaneous Speed: How fast you travel at a specific time point. Estimated by looking at very short distances and time intervals near the time of interest. - Speedometer to measure or very short Odometer and stop watch readings

Practice Problem • Problem: – If you do a road trip the east coast, it is about 1670 mi. How much earlier would you arrive if you went 80 mph rather than 75 mph on average?

Answer • Problem: – If you do a road trip the east coast, it is about 1670 mi. How much earlier would you arrive if you went 80 mph rather than 75 mph on average? Answer: We want to find the time it takes for each case. Notice that equation |v|avg = distance / time has only one unknown. Rearrange equation: time = distance / |v|avg Solve for time for each case and subtract them.

Another problem. Johnny meanders through the woods walking a speed on average of about 5 mph. After about 4 hours he is found by a police officer who informs him he is only about 3 miles from his house. What is Johnny’s average velocity?

Acceleration Average acceleration: How quickly an object changes velocity on average. - Variable: |a|avg = (vf-vi)/Δt - Units of acceleration: m/s 2 Instantaneous acceleration: How quickly an object changes velocity at a specific time. - Estimate using above formula at very close surrounding times.

Practice Problem Question: In 5 seconds a car moving in a straight line increases its speed from 50 km/h to 65 km/h, while a truck goes from rest to 15 km/h in a straight line. Which has a greater acceleration, the car or the truck? What is the acceleration of each vehicle.

Practice Problem Question: In 5 seconds a car moving in a straight line increases its speed from 50 km/h to 65 km/h, while a truck goes from rest to 15 km/h in a straight line. Which has a greater acceleration, the car or the truck? What is the acceleration of each vehicle. We want to compute the acceleration of each vehicle and compare it to the other. Use the equation|a|avg = (vf-vi)/Δt and compute |a|avg for each.

Lab Safety Quiz Turn in Homework #3 (unless you fall into the category of “I don’t have a textbook yet”) Turn in any late homework. Lab Safety Quiz starts ASAP.

Warm Up – 1 D Motion Day 2 A runner is make her way on a 20 km run and must rest for 5 minutes after every 5 km of running. If she runs an average speed of 3. 6 m/s when she is running, what is her total average speed?

Quick Review Position: Displacement: Average Speed: Average Velocity: Instantaneous Speed / Velocity: Average Acceleration: Instantaneous Acceleration:

Physics 500 In pairs – complete the worksheet (You need a calculator, stopwatch, and meter stick) - Each person makes up 2 types of races, but both group members performs 4 types of races. - Determine the average speed / velocity for each race for each person - Determine the mystery distance using one of these races.

Free Fall •

How fast? •

Practice Problem If you drop a ball from a tall cliff, what is its velocity after 3. 4 seconds? If you instead throw the ball upwards at 40 m/s, what is its velocity after 4 seconds? What is it after 5 seconds? What happened between these two times?

How far? •

Worked out Example •

Practice Problem Rank the planets by the distance a ball would fall in 2 seconds if dropped off a hovering space craft close to the surface from largest to smallest. Calculate the distances and speed for the first 3 on your list.

Graphing •