Applied Science - Physics (6A) Post Lab
 OBJECTIVES: Describing motion. Exploring the different laws of motion. VOCABULARY: acceleration centrifugal centripetal friction rotate MATERIALS: lab sheet from previous lab Students look at lab materials again.
 BACKGROUND: Students may have had trouble describing some of the motions that were observed during lab. The words below are very crucial to understanding motion, take care that students understand the scientific terms, which may be different from the common usage of the words. Rotating and spinning both refer to an object that turns on its axis. The yo-yo, gyroscope, and orbiter can be described in part as rotating on an axis. Centripetal force is an inward force or center seeking force that causes an object to follow a circular path. Centrifugal force is an outward force, the reaction to centripetal force. You are sitting in the center of the rear seat of a car. The driver suddenly turns left rounding a corner, with tires squealing, in a wide circular arc. You find yourself sliding across the seat to the right and you remain jammed against the right interior wall of the car until the driver straightens. Centrifugal force pushes you outward, but the wall of the car pushes you inward an effect of centripetal force. Speed is a basic property, and defined as a body that travels a certain distance in a given time. An automobile for example, travels so many miles per hour. Speed is simply the ratio of distance traveled per time (speed = distance/time). When we describe speed and the direction of motion we are specifying velocity. If we say that a body moves at a rate of 40 miles per hour to the north, this is velocity. Constant velocity implies constant speed and direction. A car on a circular track may have a constant speed but the velocity is changing. Any change of speed or velocity is called acceleration, In a car, acceleration would be called "pick-up." It is the rate of change, which refers to a decrease or increase of speed. PROCEDURE:    Go over the previous lab materials in more detail, using the information provided below. YO-YO - The string is not tied to the axle but looped around it. Yo-yo reaches the bottom and the yo-yo keeps rotating. The yo-you keeps spinning (sleeping) until you "wake it up" by tugging on the string causing it to climb. The yo-yo rolls down, the string with a constant acceleration as stated in Newton's second law of motion. FORCE MACHINE - For every action there is an opposite and equal reaction. When you lift one ball the energy is released when it hits the other balls. The energy goes through the balls and emerges when the last ball releases the energy. Theoretically the balls should go forever, but the energy will dissipate because of friction. BALL - Throwing the ball up toward space can be explained by Newton's first and second laws. The ball is thrown and will continue unless friction and gravity didn't force it down. The second law of motion explains the speed that a student throws it. Notice that the motion of the ball at the beginning will be different because each student will accelerate the ball differently. BALLOON ON STRING - The balloon going backwards illustrates that for every action there is an equal and opposite reaction. The balloon loses air that reacts by moving along the string. ORBITER - The orbiter can rotate on its axis (the string), but the plastic fins are pulled outward by centrifugal force and inward by centripetal force. The speed of the axis determines the shape. The faster the spin the greater the tendency to go outward. GYROSCOPE - A gyroscope is a wheel mounted so it can freely rotate in any direction. Once the wheel is spinning the mount can be turned in any direction and the wheel will continue to spin in the same plane. Unless an outside force stops the gyroscope it can continue, even if it looks like it should fall down.