Understanding Displacement in Physics: Essential Concepts

2. Physics Review Displacement

3. Free Body Diagrams A free body diagram is a pictorial representation of an object used to study the forces acting on a system. E x a m p l e A free body diagram showsonly the information requiredby the problem under study.

4. Distance versus Displacement Ending point Distance is a scalar. (It has no direction) Displacement is a vector. (It has direction) Displacement o A Starting point NOTE Displacement is the straight line directly from the starting pointto the ending point. Remember: Displacement has magnitude and direction. Click Click

5. PRACTICE

6. III II IV Displacement Slide: I An object travels the following distances: 9 m [E], 6 m [N], 4 m [W] and 2 m [S] Which of the vectors on the right represents the displacement of the object? A) I B) II C) III D) IV 4 m [W] 2 m [S] 6 m [N] Displacement 9 m [E] Not drawn to scale Click Click

7. Displacement Slide: Riding her bike, Stefania traveled the following distance frompoint-A to point-D: AB = 4.00km North BC = 11.3 km [S 45 E] CD = 8.00 km West Determine Stefania’s displacement. A) 4.00 km North B) 4.00 km South C) 23.3 km North D) 23.3 km South E) 0 Note BD = CD = 8.00 km and BA = AD = 4.00 km Click

8. Displacement Slide: The graph below represents the velocity of a butterflyas it flies across a field for 20 seconds. +235 m (forward) -90 m (backward) What is the displacement of the butterfly from the 4th to the 20th s? A) 365 m B) 325 m C) 185 m D) 145 m Click

9. Displacement Slide: To go from his house to four of his friends, James must travelin different directions as listed below: Ann: 4.8 km [N] , 3.2 km [W] Bill: 20 km [N] , 15 km [S] Chris: 3 km [N] , 7 km [S 45o E] Don: 3.5 km [S] , 1 km [E] , 2 km [S] Which friend has the greatest displacement from James’ house? NOTE We need only considerthe magnitude and notthe direction. Ann: 5.8 km Bill: 5 km A) Ann B) Bill C) Chris D) Don Chris: 5.4 km Don: 2.5 km Click

10. 20 km E < 20 km < 20 km Displacement is a vector from the starting point directly to the ending point. Displacement Slide: 0 Click

11. Answer Displacement Slide: 2 1 3 4 5 Click

12. Displacement Slide: Click

13. Starting point Ending point 2 km Displacement Slide: Click

14. Right represents North Displacement Positive velocity (above the x-axis) means going forward. The area from the line to the x-axis represents forward distance since it has a positive value. Negative velocity (below the x-axis) means going backward. The area from the line to the x-axis represents backward distance since it has a negative value. Starting point Ending point DisplacementSlide: The graph below represents the motion of an automobile as it moves northward. Determine the displacement of the automobile. Remember: displacement is the straight line from the starting point to the ending point. Forward The forward displacement is the area under the curve above the x-axis NOTE Since velocity is plotted versus time, the area to the x-axis represents the distance traveled. The backward displacement is the area above the curve below the x-axis Note that for the problem, the time stops at the ending point (t = 20 s). However, according to the graph, the automobile continues to accelerate backwards. Forward Backward Answer 160 m North Click Click Click Click Click Click

15. The End … and good luck!