Teacher notes/ activities. Gravity is the attractive force between all objects in the universe. It is the force that pulls objects to the earth.

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1 Gravity and forces unit Teacher notes/ activities Gravity is the attractive force between all objects in the universe. It is the force that pulls objects to the earth. Galileo, a famous Italian scientist who lived in the 1500's, was the first to discover the force of gravity. In his famous experiment he dropped two cannonballs, one 10 times the mass of the other, at exactly the same time from the Leaning Tower of Pisa. Which cannonball do you think hit first? Before you answer the question set up your own Galilean type experiment. 1. Find two round objects with different masses. 2. Stand on a chair and drop the two objects at exactly the same time from the same height. Explanation: Both objects should hit the ground at the same time. Even though the two objects had different masses, gravity pulls each down to the ground at the same rate. Galileo discovered that gravity accelerates all objects at the same rate. Try dropping a leaf and a rock at the same time from the same height. Which one do you think will hit the ground first? According to the above explanation, they should hit at the same time, but the rock hits first. Why? Both of these objects are still being accelerated by gravity at the same rate but, in this case, since the leaf has a small mass and a large surface area, air resistance is able to oppose the force of gravity and slow the leaf down. Safety concerns: Teachers and students, be sure to use safe operating procedure when dropping the objects to make sure that no one is in the path of the falling objects!

2 Forces A force is a push or a pull. Force gives an object the energy to move, stop moving, or change direction. When you write with a pen you exert a force. When you peddle your bike, blow your nose, turn on a faucet, chew your gum, or swimming in a pool, you are exerting forces on other objects. We would never be able to move without exerting forces on things. Other examples are: * A flag being blown by the force of the wind. * Iron being pulled towards a magnet. * A jet engine propelling an airplane forward. Friction is a force that opposes motion. Friction acts in a direction opposite to the object's direction in motion. Without friction, the object would continue to move at a constant speed forever. There are different forms of friction. One type is called sliding friction. This is when two surfaces slide one over the other. A snow boarder slides over the snow covered slopes using sliding friction everyday. When an object rolls over a surface, the kind of friction that occurs is rolling friction. Skate boarders take advantage of this type of friction all the time. Reducing the amount of friction between the surface and the wheels allow skaters to go really fast. Friction also occurs in fluids (gases and liquids). This is how a surfer glides over the water or a shark glides through the water. This type is called fluid friction. Balanced and Unbalanced Forces A force is a push or a pull. A force can give energy to an object causing the object to start moving, stop moving, or change its motion. Motion, like that of your skateboard, is a result of unbalanced forces. If you and a friend were in an arm wrestling match and you were dead even, your stationary arm position would be an example of a balanced force. If you suddenly gained the advantage over your friend, it would be an example of motion resulting from an unbalanced force. Newton s 3 laws First law Sir Isaac Newton lived during the 1600s. Like any good scientist, he made observations about the world around him. Based on his observations he developed his now famous three laws of motion. Although he lived hundreds of years ago, his work continues to be viewed as one of the most important contributions to science. His laws of motion explain rest, constant motion, accelerated motion, and describe how balanced and unbalanced forces act to cause these states of motion.

3 Have you been riding in a car when the driver suddenly slammed on the brakes? How did your body move as the car came to a stop? You probably felt your body move forward. When you felt this happening you experienced Newton's first law of motion. Newton's first law of motion says that an object in motion will stay in motion and an object at rest will stay at rest unless acted on by an unbalanced force. In the car your body was in motion, traveling at the same speed as the car. When the car stopped, your body stayed in motion. If you were not wearing a seatbelt and you were traveling very fast, your body could continue to move forward through the windshield! Newton called his first law inertia. Try the following activity to demonstrate this law! 1. Place a 3x5 card on top of a glass. 2. Put a coin on the center of the card. 3. Flick the card horizontally with your finger. 4. What happens to the coin? 5. Explain what happened to the coin using Newton's first law. This activity is similar to the magician's trick of pulling a tablecloth out from under dishes on a table. Because the dishes have inertia, they will stay at rest unless acted on by some unbalanced force. If the tablecloth is really smooth and is pulled out fast enough, there is not enough friction created to cause the dishes to move. DO NOT TRY THIS AT HOME WITHOUT PARENT PERMISSION! 2 nd law If a bowling ball and a soccer ball were both dropped at the same time from the roof of a tall building, which would hit the ground with a greater force? Common sense tells us that the bowling ball would. We know that gravity accelerates all objects at the same rate, so both balls would hit the ground at the same time. Therefore the difference in forces would be caused by the different masses of the balls. Newton stated this relationship in his second law, the force of an object is equal to its mass times its acceleration. A karate master can exert a tremendous force by utilizing years of training, proper technique and focus. Although a human hand and forearm may have a mass of.75 kg, with proper technique, a karate sensei (master) will be able to use his entire body's mass in breaking bricks. Combining a possible mass of 70 kg and a acceleration of 50 m/s2, this master will exert 3500 N of force, well more force needed to break several bricks.. A speeding bullet and a slow moving train both have tremendous force. The force of the bullet can be attributed to its incredible acceleration while the force of the train comes from its great mass.

4 3 rd law Imagine a rocket is being launched from the earth. Hot gases are pushed out from the bottom of the rocket as the rocket is thrust upward. The force of the gases pushing against the surface of the earth is equal and opposite to the force with which the rocket moves upward. The motion of the rocket can be explained by Newton's third law, for every action there is an equal and opposite reaction. In other words, when one object exerts a force on another object, the second object exerts a force of equal strength in the opposite direction on the first object. Likewise, when a skeet shooter fires his shotgun at a clay disc flying through the air, he experiences the recoil upon the shotgun. The "kick" felt by the shooter is the reaction force upon the shotgun which is equal in magnitude to the force that pushes the pellets. The following simple activity will help you investigate Newton's third law. 1. Blow up a balloon. 2. Hold the opening downward and release the balloon. 3. Repeat this several times, and observe what happens. 4. Now describe what happened using Newton's third law of motion. Forces lab Marshmallows Away Activity There She Throws This is a great way to demonstrate kinetic and potential energy as well as simple machines. Each student will design and construct a working catapult that will launch a large marshmallow the farthest distance possible along the straightest path possible. This project is worth 50 points. To receive full credit, your device must successfully launch a marshmallow a minimum of 5 feet. Procedures Rules: 1. The dimensions of the catapult will not exceed one cubic feet (12" high X 12" wide X 12" deep) in size for the base. The Lever arm may not exceed 2 feet. 2. You may power your catapult by any means possible. Such as rubberbands, counterbalance weights, or elastic lever arms.

5 3. The winner of the throwing competition is the student that launches the marshmallow the farthest and the straightest. Conclusion Have students complete the calculation sheet during the contest. Lab 2 Roller coaster lab Standard: Students will relate forces and energy to motion. Objective: The student will identify the role of energy in motion. Objective: Analyze energy movement and transformation. Intended Learning Outcomes: 1a. Make observations and measurements (uses instruments as appropriate). 2a. Identify variables and describe relationships between them. 2c. Plan field studies, controlled experiments, and other investigations. 4b. Understand how technological advances have influenced the progress of science, and how science has influenced developments in technology. 4d. Recognize the personal relevance of science in daily life. This is a great activity to teach about energy conversion from Kinetic to Potential energy and back again. Using the materials provided, build a working roller coaster with all the required components. Students must demo their team's coaster to the class and draw their individual blue prints of their ride. This activity is worth 60 pts. Materials (per team) 1-15 foot polyvinyl tube 1/2" dia. 3 - Ring Stands w/ 48" dowel 1 - roll of masking tape 3/4" wide 1 - Film Canister 2 - Steel bearing (must fit in tube easily) identified coasterrequirements 1. Name your roller coaster. (5 pts.) 2. Each roller coaster must have the following components - * Two loops (10 pts.) * Two true hills (10 pts.) * One corkscrew or twist (10 pts.)

6 * Extra credit: Double flat spiral (10 pts.) 3. Each roller coaster must be drawn-up like a blue print. (20 pts.) 4. Included on the drawing: The following must be included on all hills, twists and loops. * Highest Potential Energy (Hi Ep ) * Lowest Potential Energy (Lo Ep ) * Highest Kinetic Energy (Hi Ek ) * Lowest Kinetic Energy (Lo Ek ) * Where rider would feel weightless. (-G) * Where the forces of gravity is greater than one. (+G) Background Form a group of three to four students. Allow the students to place their ring stands on the desk or tables. Set the maximum height a ride may begin. Do not allow them to begin the ride any higher because this will give an unfair advantage by allowing them greater potential energy at the start. Have the students tape the film canister to the end of the tube to prevent the loss of the steel bearing after rolling it through the tube. Have fun with this activity. Conclusion 1. Demonstrate your ride by: a. Stating the rides name. b. Identifying the components of the ride (hills, twists,&;loops) c. Identifying the impact of forces on the ride (Ep, Ek, -G, +G) d. Successfully completing the ride with your steel bearing. Safety: There are no safety concerns with this activity.