Lab: Centripetal Force

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Lab 2 of 2LB
Lab 1 of 40B
Centripetal Force 1-28-99

Courtesy of Benli Young

The Main Goal:

We are going to verify the equation of force equilibrium between the Centripetal Force and the gravitational Force, M_Tw²R=M_hg.

Later, by filling out the following data table, see how well you have measured!

THE "SLOPE" TABLE

procedure	Graph	R, UNIT:( )	M_h, UNIT:( )	M_T, UNIT:( )	Unit of slope	Theoretical Slope	Measured Slope	%error
12	w² vs. 1/R	N.A.				gM_h(1/M_T)=		%
13	w² vs. M_h		N.A.			g(1/M_T)(1/R)=		%
14	w² vs. 1/M_T			N.A.		gM_h(1/R)=		%

It is better to use that gravitational constant, g= 9.80C10²(cm/sec²).

(Procedure 1)

Prepare and weigh the trolley, hanger and all masses.

Item	Mass, Unit:( )
Hanger
Trolley
The 100-gram mass
The 50-gram mass
The 20-gram Weights
The 10-gram mass
The 5-gram mass

(Procedure 2)

Add 50g onto the trolley.

Put 45g on the hanger.

(Procedure 8)

Print out ONE AND ONLY ONE sample "w versus Time" graph (like Fig.3).

On your print-out, you must indicate every proper detail like "M_T", "M_h", "R", and the local minimun "w", etc., associated with your graph.
TIP: To locate the exact value of the local minimun "w" on your "w versus Time" graph, it is very useful to follow these modified steps.

Look at the right end of this curve. See if there are some points lower than the local minimun "w" on your graph.
If there are, then try to delete those lower points. At the end, make sure that there is only one local minimun w point on the whole curve.
Once the former local minimun "w" turns into the real minimun point on screen, press "ENTER" key on your keyboard.
Go to option "T" to display the whole data table.
Press "END" key on your keyboard.
Look at the button of "STATISTICS.
On the row of "Min", you will find out the exact value of the minimun "w", which is the real critical "w" when the Centripetal Force is equal to the gravitational force acting on the hanger.

(Procedure 10,11,12)

(OPTIONAL)Total trolley mass M_T= _______ (trolley mass) + 50g = ____________, UNIT:( )

(OPTIONAL)Total hanging mass M_h = ________ (hanger mass) + 45g = ___________, UNIT:( )

Choose at least 5 rows in the following R and w data table. And mark those rows.

	R, UNIT:( )	w, UNIT:( )

	10

	15

	20

Plot out w- R graph on screen only.

Print out w²-1/R graph.

(0.5): On your print-out, you have to indicate the proper details like "M_T", "M_h", etc., associated with your graph.

Go to THE "SLOPE" TABLE and fill out the corresponding row.

(Procedure 13)

(OPTIONAL)R = ____________, UNIT:( )

(OPTIONAL)Total trolley mass M_T= _______ (trolley mass) + 20g = ____________, UNIT:( )

Choose at least 3 rows in the following M_h and w data table. And mark those rows.

	M_h, UNIT:( )	w, UNIT:( )


	20

	30

(0.5): Print out w²-M_h graph.

(0.5): On your print-out, you have to indicate the proper details like "R", "M_T", etc., associated with your graph.

Go to THE "SLOPE" TABLE and fill out the corresponding row.

(Procedure 14)

(OPTIONAL)R = ____________, UNIT: ( )

(OPTIONAL)Total hanging mass M_h= _______ (hanger mass) + 20g = ____________, UNIT: ( )

Choose at least 3 rows in the following M_T and w data table. And mark those rows.

	M_T, UNIT: ( )	w, UNIT: ( )


	113

	163

(0.5): Print out w²-1/M_T graph.

(0.5): On your print-out, you have to indicate the proper details like "R", "M_h", etc., associated with your graph.

Go to THE "SLOPE" TABLE and fill out the corresponding row.

Questions: (4 points)

Question 1: (1 POINT)

Do the masses of the track or the disk matter?

Requirement:

(0.5): In a reflection, just write "YES" or "NO", now.

(0.5): Please offer at least one reason.

Question 2: (1 POINT)

What role does friction play in the experiment?

Requirement: According to the TA manual, there are mainly two kinds of friction. Please elaborate them.

(0.5): Friction in the axis and the smart pulley allowes us to see the effect of trolley sliding inwards. It will help our measurement. Please explain the mechanism.

(0.5): Friction in the trolley itself, and in the string and pulley at the axis, will have bad influence. Please explain why.

Question 3: (You do not need to answer this question. It is for your reference only!)

Why is the angular velocity at the bottom of the dip be the appropriate angular velocity to use in the experiment?

ANSWER: According to the TA manual, here is an explanation for your reference.

Because this is the angular velocity at which the trolley just starts to roll inwards. It is the angular velocity at which the inwards force from the hanging mass begins to overcome the outward centripetal force.

Question 4: (2 POINT)

How well do your measurements agree with expectations?

Requirement:

(0.5): In a reflection, just write "YES" or "NO", now.

(1.5): Please look at the last column of THE "SLOPE" TABLE. You must offer at least one quantitative explanation for each slope you have. And it is better in percentage.

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