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 juryrigged 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


C-clamps were used for stability.
Another clamp is used to hold
the ball and drop it consistently.
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
Acceleration Calculations

By Newton’s Second Law,
F=ma=(0.05943kg)(-769.0m/s2)
≈-45.7N