Physics

Slides Slides Minutes1 9 272 Vectors 13 393 Kinematics 13 394 Graphs 10 305 Energy 10 306 Power 5 157 Springs 4 128 Shadows 3 99 Field of Vision 7 2110 Colors 3 911 Concave mirrors 7 2112 Convex mirrors 4 1213 Refraction 5 1514 Lenses 10 3015 Optical Power 6 18

Displacement

Free Body DiagramsA 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.

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Distance is a scalar. (It has no direction)Displacement is a vector. (It has direction)

Displacement is the straight line Displacement is the straight line directly from the starting pointdirectly from the starting point

to the ending point.to the ending point.

NOTE

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Starting point

DisplacementEnding point

Ao

Remember: Displacement has magnitude and direction.

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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 representsthe displacement of the object?

A) I B) II C) III D) IV

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Not drawn to scale9 m [E]

6 m [N]

4 m [W]2 m [S]

Displacement

II III

IIV

Displacement Slide:

A) 4.00 km NorthB) 4.00 km SouthC) 23.3 km NorthD) 23.3 km SouthE) 0

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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.

NoteBD = CD = 8.00 km

andBA = AD = 4.00 km

Displacement Slide:

The graph below represents the velocity of a butterflyas it flies across a field for 20 seconds.

A) 365 mB) 325 mC) 185 m

D) 145 m

What is the displacement of the butterfly from the 4 th to the 20 th s?

+235 m (forward)

-90 m (backward)

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?

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A) Ann B) Bill C) Chris D) Don

Ann: 5.8 kmBill: 5 km

NOTEWe need only considerthe magnitude and not

the direction.

Chris: 5.4 kmDon: 2.5 km

Displacement Slide:

20 km E< 20 km

< 20

km

0

Displacement is a vector from the startingpoint directly to the ending point.

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Displacement Slide:

12

3

45

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Displacement Slide:

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Displacement Slide:

Starting point

Ending point

2 km

Disp

lace

men

t Sl

ide:

The graph below represents the motion of an automobile as it moves northward. Determine the displacement of the automobile.

NOTESince velocity is plottedversus time, the area

to the x-axis representsthe distance traveled.

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.

Startingpoint

Endingpoint

DisplacementThe forward displacement is the area under the curve above the x-axis

The backward displacement is the area above the curve below the x-axis

Right represents North

160 m North

Forward Backward

ForwardRemember: Remember: displacement is the displacement is the

straight line from the straight line from the starting point to the starting point to the

ending point.ending point.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.ClickClickClickClickClickClick

Displacement Slide:

… and good luck!