Figure M4
Thruster
The frame may be cut from one piece of corrugated cardboard 36 cm long,
or made from two separate pieces 18 cm long. These dimensions accommodate
the springs in your kit. The lines of corrugation must run the long way.
For more details about building a Thruster,look at the
Thruster Plans which have dimensioned drawings.
Thruster Calibration
The Thruster is a tool for measuring unknown forces and applying known forces.
All the Thrusters will be different, so each one must be calibrated; we
must agree on a standard.
For this calibration we will use the pull of earth's gravity on some
mass we agree upon. Physicist
use kilograms and grams of masses. Your class could use pennies or nickels
for mass instead of metric masses. ( One penny is about 2.5 grams and one
nickel is about 5 grams. )
For force, physicists use Newtons. The earth's pull on one gram is about
0.01 Newtons so the pull on 100 grams is about 1 Newton (0.980 N). The Thruster
is designed for a maximum force of about 1.5 Newtons, so a 50 g, and 100
g mass would let you determine the spring compression for 0.5 N, 1.0 N,
and 1.5 N respectively. Use one edge of the spring-stop bead for a force
pointer, mark a zero reference point on the frame beside the spring slot.
You could glue a clean white strip of paper beside the spring slot for the
force markings. Pull the plunger down, compressing the spring, with a 50
g mass, and mark the location of the force pointer on the frame beside the
spring slot. Repeat this with 100 g, and 150 g. Label these marks zero,
0.5 N, 1.0 N, and 1.5 N. Divide up these 0.5 Newton marks, by eye, with
five subdivisions (one subdivision = 0.1 Newtons) and you are ready to measure
an unknown force or push with a known force.
Thruster Energy
This is an investigation to establish a mathematical relation between the
compression of the Thruster spring and the distance it can shoot a puck.
You need a calibrated thruster and a puck. One way to build a puck is to
glue three 6 cm diameter circles of corrugated cardboard. You could also
use a jar cap. A long, smooth, flat surface is necessary; if everyone in
class uses the same surface, you can have a contest. The main part of this
investigation is the collection of a set of measurement pairs, maximum thruster
forces and sliding distances. You could measure slide distances for maximum
forces of 0.25 N, 0.50 N, 1.00 N, 1.25 N, and 1.50 N. Record your measurements
in a table and plot them on a graph. This all sounds easy, but you may discover
that the slide distance is not always consistent. You may need to make several
shots at each maximum force and average the slide distance. Record all your
measurements, but list and graph only the averages. When you graph recall
that the maximum force is the variable which you choose, so it is the independent
variable and would normally be plotted horizontally. The slide distances
would then be plotted vertically as the dependent variable. Can you express
this relationship mathematically?