PHYSICS 125 Experiment #6 Conservation of Energy

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Instructor: Partners:

Date Performed: 10/12/2023 Comments:

Date Submitted:

OBJECTIVE

Conservation of energy will be demonstrated in this lab by comparing the potential energy lost by a falling mass to the potential energy gained by a spring to which the mass is attached.

EQUIPMENT

Meter stick & masking tape

Hooked Masses Set

Spring support & stand

Spring Figure 1

INTRODUCTION

The law of conservation of energy is one of the important principles of Physics.

It requires that in energy transformations (for a closed system), it is possible to account for all energy gains and losses. Lifting a mass to some height requires a force through a distance.

W=Fs

In other words, work must be done on the mass. At its new height, the mass has an increase in its potential energy.

P.E.=mgh

To stretch a spring, a force must be exerted through a distance. The stretched spring then has gained a potential energy equal to the work done to stretch the spring. (W=Fs)

To calculate this work, the average force between two points of stretch for the spring must be used. The average force is the middle force, or the initial force plus the final force divided by two. This occurs because of Hooke's Law which states that the stretch of a material such as that used in a spring and the force to stretch a spring are uniform and proportional over a range of values. Average force (F/2) times the distance (s) then is Fs/2, or work, which is the area under a force-distance graph. The energy for the fallen mass can then be compared to the energy of the stretched spring found from the area under the spring's force-distance graph.

PROCEDURE

1. Suspend the spring from the support as shown in Figure 1.

1. Put a 500g mass on the unstretched spring and allow it to fall. Record the lowest point to which the mass falls. Perform several trials to determine the lowest point with fair certainty.Average these trials in Table I.

1. Add small weights until the spring starts to stretch. Locate a zero position or reference position for the spring in this position. Use the same point of reference for all following measurements. (The very bottom of the spring should serve as a consistent reference point.)

1. Hang an additional 100g mass on the spring.Determine the new position of the reference point and the distance (s) the spring was stretched. Convert the masses to forces and enter the force and distance values in Table II below.

1. Repeat step 4 using weights of 100g increments until the total elongation is greater than the average distance fallen in Table I.

1. Using the data from Table II, draw a Force v Distance graph, placing the Force on the

y-axis and Distance on the x-axis.

Table I		Table II
Trial #	Distance Fallen		Mass (kg)	Force (N)	Distance Elongation (m)
1	.61m		0	0	0
2	.61m		.1kg	1N	.15m
3	.61m		.2kg	2N	.26m
Average	.61m		.3kg	3N	.40m
		.4kg	4N	.49m
		.5kg	5N	.61m
		.6kg	6N	.71m
		.7kg	7N	.81m
		.8kg	8N	.91m

QUESTIONS

1. Calculate the potential energy lost by the falling mass using data from Table I.

1. Using data from Table II, find the energy gained by the stretched spring at the distance of the fallen mass. The spring may not be linear near zero but that may be ignored when finding the area by assuming the graph is a straight line. The energy gained is the triangular area under the graph up to the distance stretched for the fallen mass. Show your calculations on the graph.

1. Compare the energies of questions #1 and #2 above.Does the work found as the area under the graph equal the loss in potential energy of the falling mass?What happened to the work done on the spring by the falling mass?

1. Explain how the experiment demonstrates Conservation of Energy.

This experiment demonstrates Conservation of energy by comparing the potential energy lost by a falling mass to the potential energy gained by a spring to which the mass is attached.

a concluding statement for this experiment.