This is a group task that can help children visualize the concept of uniform circular motion. Give a blank 3 x 3 inch sheet to each of the students and ask them to use their compass and ruler to draw a circle with a one-inch radius, split in half by a horizontal diameter line, in the middle of the paper. Divide 360 -- the degrees of a circle -- by the number of students to find "Q." Ask the student sitting closest to you place the protractor's straight side on the circle's diameter, measure Q degrees and draw a small sphere on the circle's circumference. The next student must measure 2 x Q degrees on his sheet before drawing a sphere, the third student must measure 3 x Q degrees and so forth. Collect all sheets and place them one over the other in reverse order. Staple one side of the sheets together and flip through the booklet, showing the animation to students. As the distance travelled by the ball between sheets remains the same, the animation depicts a circular motion animation.
Give a piece of string to each student, along with a marble ball, sticky tape, and a red and green sheet of foam paper. Instruct the students to cut out a red and a green arrow from the foam sheets. Students must then use sticky tape to attach one end of the string to the marble and loosely tie the other end of the string on a pencil. Instruct children that they must stick the red foam arrow -- acceleration -- on the string, directly next to the marble ball but pointing towards the pencil, and the green arrow --velocity -- perpendicular to the stretched string and pointing towards the motion's direction. Students must hold the pencil upright but firmly on their desk, while giving a boost to the marble ball to reproduce a uniform circular motion. Through this activity, children can understand how changes in direction affect velocity.
The velocity vector shows the direction of the object at every given moment. This means that if we cut the string, the marble ball would move toward the direction the green arrow was pointing. It is difficult -- and dangerous -- to cut the string while the ball is moving, so use two cream pail lids for this task. Remove a 20-degree section from one lid's circumference. Give the two lids, along with a marble ball, to one student at a time. Ask the student to place the ball on the untouched lid and roll it around, trying to visualize the green velocity arrow. The student must then place the ball in the lid with the hole and roll the ball around to see if his prediction on the direction of the ball is confirmed. Give every student the opportunity to use the lids and predict the direction of the ball.
Classroom experiments can show students the basics of uniform circular motion, but it is difficult to change the variables, such as mass of the object, radius and speed, to examine the effects. For this purpose, you can use computer simulations, such as the "Uniform Circular Motion" Shockwave application on The Physics Classroom website. Ask children to change the variables according to your instructions and report the effects on the velocity and acceleration vectors. If the number of computers at your school is not sufficient for individual practice, divide the class into groups.