Voltage Probe Force Lab

1
Voltage Probe Force Lab

• by Kevin Bell and Christopher Nield

2
The Problem

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

3
The Experiment

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

4
The Experiment

• ?v 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.

5
The Experiment

• Measuring ?t 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.

6
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.

7
The Lab

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

8
The Setup

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

9
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.

10
The Setup

• The ball wrapped in wire

11
The Setup

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

12
The Setup

• The ball completing the circuit

• The ball must be massed for later analysis

13
The Setup

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

• C-clamps were used for stability.

14
The Experiment

• A quick twist drops the ball without added force

• From there, it drops to the tennis racket setup

15
The Experiment

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

16
The Data Analysis

• Average contact time (?t) 0.00975s
• Ball mass (m) 0.05943kg
• Calculated acceleration (a)-769.0m/s2
• By Newtons Second Law,
• Fma(0.05943kg)(-769.0m/s2)
• -45.7N

Acceleration Calculations
17
Calculations
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