Name_________________________

STUDENT INSTRUCTION AND ANSWER SHEET

Activity 2: Concept Introduction- The Hammer Throw

A. Watch the video of the hammer throw (top view).
(Note: your teacher may have already downloaded this movie for you)

B. Watch the video of the hammer throw (side view).
(Note: your teacher may have already downloaded this movie for you)

C. Is the thrower able to stay in one location as the hammer is swung around? What object or force is causing the thrower to move from side to side as he spins?

D. Draw four overhead sketches (like the drawings provided in Activity 1 of the Sun and Jupiter) of the hammer and thrower for four different instances during one complete orbit. Include dotted circles with each sketch to illustrate the entire path of the orbit for both the hammer and thrower (as was shown in the drawings provided in Activity 1).

E. In each drawing mark the center of the orbit for each object.

F. Should the centers of each object's orbit lie at the same location? If so, what is the name given to this location? If not why not?

G. Is the location you marked closer to the thrower, the hammer, or halfway between the two? Explain your reasoning.

H. If a more massive hammer is used, does the location of the center of mass move closer to or farther from the hammer? Does the location move closer to or farther from the thrower? Draw a sketch to illustrate your answer.

I. Compare the size of the orbital paths (circles) that you drew in question D to those that you drew in question H. Did the size of each object's orbit increase, decrease or the stay the same?

J. If the mass of the hammer and thrower are equal how does the distance from the center of mass to each object compare? Draw a sketch to illustrate your answer.

K. The equation provided below is used to calculate the location of the center of mass for a two-body system. For the thrower & hammer system shown let the mass of the thrower m₁ = 120 kg, the mass of the hammer m₂ = 40 kg. The distance from the origin to the thrower is represented by the symbol r₁ and the distance from the origin to the hammer is represented by the symbol r₂. The values of r₁ and r₂ can be negative. The hammer and thrower are 1.5 m apart.

i. Calculate the location of the center of mass for a coordinate system with the origin chosen to be at the midpoint between the hammer and thrower. Show your work and mark this location in the drawing above.

 

ii. Calculate the location of the center of mass for a coordinate system with the origin chosen to be at the location of the hammer. Show your work and mark this location in the drawing above.

 

iii. Calculate the location of the center of mass for a coordinate system with the origin chosen to be at the location of the thrower. Show your work and mark this location in the drawing above.

L. Does the actual location of the center of mass change with the different choices of coordinate systems?

M. The top-view path for one orbit of the thrower is shown below, the location of the hammer has not been drawn. Using the length and size of the rope and hammer shown below mark the location of the hammer for each position of the thrower.

N. With each thrower location, are there any other locations that the hammer could have been drawn at other than the one you have shown? Why or why not?

O. At each location 1-4, draw a vector to represent the velocity of the thrower.

P. If you were standing at point A, for which position(s) of the thrower would you measure the radial velocity to be:

i. positive
ii. negative
iii. zero

Explain your reasoning.

Q. Carefully sketch a radial velocity vs. time graph for the thrower as seen by an observer at point A.


R. How would you change the above graph if it were made by an observer at point B? Explain your reasoning.