# Hands-On-Physics MECHANICS

## - Introduction -

• Background: Things to think about as you Mess Around
• Questions: Challenge questions which the Messing Around research is designed to answer
• Tools: List and description of tools available for this activity
• Materials: List, description, and suggestions for use of materials available for Messing Around
• Activities: Hands-on activities which are components of the Messing Around research
• Reporting: Suggestions for collecting, synthesizing, and reporting the work done while Messing Around

### Background

The measurement of speed is central to the understanding of motion. We are all familiar with speed and many people enjoy high speed so much that they race. You know what speed is even if you don't know how to quantify it. Average speed is defined as the ratio of the distance travelled to the time it took to travel that distance; symbolically dist / time. While messing around, you will calculate several average speeds by measuring the distance and time.

### Questions

• What has to be measured to determine speed?
• How is motion described if speed is changing?
• How does force effect speed?
• What is the fastest speed you can measure?
• What experimental design changes might allow a faster speed measurement?
• Is there a fastest speed?

### Tools

To determine the speed of a very fast moving object, either long distances or short times must be measured. For relatively slow motion, a stop watch and measuring tape are sufficient to measure average velocities. To analyze motion in which the speed may be changing, a stopwatch which can measure several times in rapid succession. HOP uses a "lap" timer with a memory for nine separate lap times. For the third activity you build a tool for measuring force. This construction of this "Thruster" requires a hot glue gun and a sharp knife.

### Materials

Two of these messing around activities require only a soft object to drop and throw and a human runner. Making nested boxes is good practice with cardboard construction before you build a Thruster. The Thruster is made from corrugated cardboard, some springs, and a wooden rod.

### Activities

• Nested Boxes
Hands On Physics requires you to build much of your own apparatus for studying physics. The construction of good working tools requires some craftsmanship, and craftsmanship requires some experience. Hands On Physics also requires teamwork. This skill building activity is designed to give practice using cardboard and hot-glue for construction, as well as practice working as a team.

• Average Speed
Use Single time interval measurements to find the speed of several moving objects; a running person, a falling object, and a thrown object.

• Changing Speed
Measure multiple time intervals using "lap" timer to analyze the motion of a person who first walks and then speeds up to a run.

• Spring Thruster
Build and calibrate a spring thruster for comparing forces and pushing. Use the thruster to study the effects of push on the motion of a puck.

### Reporting

A record of your messing around in mechanics might include a short written description of each motion measurement. Diagrams are also helpful for explanation. Whenever measurements are made this data must be recorded carefully and accurately, with units included for clarity. Tables are useful for repeated similar measurements. To make the logic of your calculations clear, first record the formula you used, then show the numbers used to evaluate the formula, and finally record your answer.
Example: An apple was dropped and its average falling speed was determined.
Height of drop (h) = 6 feet
Time for drop (t) = 0.5 seconds
The average speed of the apple = distance/time = h/t = 6 ft/0.5 sec = 12 ft/sec
Notice that the measurements in this example are given with only one significant digit of accuracy. The result of the calculation is therefore a rough approximation. Reporting measurements to three significant digits of accuracy gives a much more useful result. A more careful measurement might give; h=5.37ft and t=0.347sec. The average speed would then be calculated to be 15.5 ft/sec. To measure changing speed, multiple measurements must be made. In this case, a table is helpful for keeping order.

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