A projectile is any object that is thrown, launched or shot, such as a golf ball, an arrow or a space shuttle. Two properties affect projectile motion: gravity and air resistance. Students can perform a variety of projects to test their understanding of projectile motion, using physics to explore and calculate the trajectories of these objects.

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## Hit the Target

Try to place a cup in the spot where a marble rolling off a table will land by using the physics of projectile motion. Set up a ramp at one end of a table and secure it in place. Hold a marble at the top of the ramp and let it go to the bottom. Determine the velocity of the marble when it reaches the end of the ramp by timing how long it takes the marble to reach the bottom of the ramp several times and taking the average. Multiply the average time by twice the length of the ramp to find the final velocity. Next, find the time it will take the marble to drop from the height of the table to the floor by multiplying the height of the table by two, dividing that quantity by the gravitational constant and taking the square root of that quantity [t = sqrt(2h / g)]. Multiply this time and the final velocity from the first step to calculate how far the marble will travel horizontally (D = VT). Set up a cup in the spot where your calculations predict the marble will land, then let the marble go and see what happens. Note any reasons why the marble may not fall in exactly the spot you calculated.

## Paper Airplanes

Construct paper aeroplanes with varying centres of gravity to determine which can fly the farthest. Use printouts or step-by-step instructions to create several paper aeroplanes with the same shape and weight. Attach a paper clip to each aeroplane at a different part of the body, such as the nose, the middle, the back and the wing. Set up a tape measure or meter sticks on the ground and see how far you can get each plane to fly. You can also vary the weight of the projectiles and see what effect this has on their trajectory.

## Falling Objects

You can reproduce Galileo's famous experiment by letting various objects fall from a certain height at the same time and calculating their acceleration or the time it takes them to hit the ground. For example, collect various pieces of fruit and lay out newspapers on the floor near a chair. First, hold two of the same fruit, such as two oranges, out in front of you. Let them drop at the same time and see whether they hit the floor at the same time. Then drop two different fruits, such as an orange and a grape and see whether there is any difference. You can also use different shaped objects, like a sheet of paper, a feather, a heavy ball or a book. Investigate why some objects may not fall as quickly, even though all objects experience the same gravitational pull.

## Wind and Angle

Determine how wind speed and launch angle affect the trajectory of a projectile, such as a bottle rocket or a water balloon. Set up a launch system outside, either using an air tank and a rocket launcher or a water balloon cannon. Measure the wind speed with an anemometer. Set the launcher with a protractor at a certain angle, such as 30 degrees, and fire a shot. Measure how far the projectile travelled straight and to the side. Run two to five more tests at different angles, such as 40, 50 and 60 degrees. Repeat the test using the same angles on another day with a different wind speed. See how each variable affects the trajectory. Make sure all the rockets or balloons are of equal weight and size.