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Voltage Probe Force Lab. by Kevin Bell and Christopher Nield. The Problem. Determine the force with which a tennis racket acts on a tennis ball. The Experiment.

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Voltage Probe Force Lab

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Voltage Probe Force Lab

by Kevin Bell and Christopher Nield

The Problem

• Determine the force with which a tennis racket acts on a tennis ball.

The Experiment

• To calculate force, it is necessary to determine the time duration during which the ball and racket are in contact (Δt) and the and the change in velocity during this time (Δv)

The Experiment

• Δv could be measured with photogates, but to keep our lab simple we calculated the change based on the height from which the ball was dropped and assuming no air resistance and perfect elasticity.

The Experiment

• Measuring Δt is more difficult.

• To do this, we considered the possibility of using a setup in which the ball would complete an electrical circuit while in contact with the racket that could potentially activate and deactivate the timer.

The Setup

• Instead of a jury-rigged timer setup, however, we found that the Vernier voltage probe was capable of highly precise measurements of voltage against time.

The Lab

• We wrapped a tennis ball with uninsulated copper wire to make it conduct electricity.

The Setup

• We then laced more wire through the strings of the tennis racket.

The Setup

• We then attached the racket wires to a battery and the voltage probe, such that the wire on the ball completed the circuit and registered as a voltage spike.

The Setup

• The ball wrapped in wire

The Setup

• Alligator clips attached to the wire on the racket, the voltage probe electrodes, and the battery

The Setup

• The ball completing the circuit

• The ball must be massed for later analysis

The Setup

• Another clamp is used to hold the ball and drop it consistently.

• C-clamps were used for stability.

The Experiment

• A quick twist drops the ball without added force

• From there, it drops to the tennis racket setup

The Experiment

• The contact time of the ball and racket can clearly be seen in the voltage spike.

The Data Analysis

• Average contact time (Δt): 0.00975s

• Ball mass (m): 0.05943kg

• Calculated acceleration (a):-769.0m/s2

• By Newton’s Second Law,

F=ma=(0.05943kg)(-769.0m/s2)

≈-45.7N

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