1103 Period 5: Newton s Laws of Motion

Transcription

1 Name Section 1103 Period 5: Newton s Laws of Motion 5.1 What Are the Four Fundamental Forces? 1) Defining the fundamental forces: Based on your class activities and your instructor s explanation, give examples of each of the fundamental forces. a) Gravitational Force b) Electromagnetic Force c) Strong Nuclear Force d) Weak Nuclear Force 2) Applications of the electromagnetic force: a) The space between an atomic nucleus and its electron cloud is so great that the majority of the volume of an atom is empty space. Since atoms are mostly empty space, explain in terms of fundamental forces why a solid object sitting on a table does not fall through the table. b) Since all objects contain positive and negative electrical charges, shouldn t we feel an electromagnetic force from every object we encounter? Explain why we do not. c) Group discussion question: Which of the fundamental force(s) is/are responsible for the force of friction? 25

2 5.2 How Do Newton s Laws of Motion Describe Forces? 3) Newton s First Law: Your instructor will demonstrate a metal cart on an air track, which minimizes the amount of friction between the cart and the metal track. a) If the cart s speed is constant as it moves along the track, is there a net force acting on the cart? b) Is a net force required to keep the cart moving at a constant speed? Explain why or why not. 4) Newton s Second Law: F = M a A Lamborghini Diablo sports car can accelerate from 0 MPH to 60 MPH in 4.3 seconds. The mass of the car is 1,580 kg. Calculate the force (in newtons) needed to accelerate the car. (We assume that its acceleration is constant.) a) Convert 60 miles/hour into meters/second. Hint: 1 mile = 1,609 meters. b) Find the acceleration of the car using v a final v t initial c) Use Newton s second law to find the force on the car during its acceleration. 26

3 Name Section 5) Newton s Third Law: Your instructor will demonstrate a cart with a fan attached to it. Before you see each demonstration, predict the cart s motion. a) When the fan is turned on, will the cart move in the direction the fan blows, move in the opposite direction that the fan blows, or not move? Prediction: Watch the demonstration and describe what happened. Explain the motion of the cart in terms of Newton s third law. b) Your instructor will place on the track a second cart with a metal sail attached. When the fan on the first cart is turned on, it blows against the sail on the second cart. Will either cart move when the fan is turned on? Prediction: Describe and explain what happened. c) Next, we connect the two carts together. Will the carts move when the fan is turned on? Prediction: Describe and explain what happened. d) With the two carts still connected, we block the air from the fan by placing a book between the fan and the sail. When the fan is turned on, will the cart move? If so, in which direction? Prediction: Describe and explain what happened. e) Group Discussion Question: You and your friend are each standing on a skateboard and are facing each other. You are playing a game of catch by tossing a five pound ball back and forth. What happens to the motion of the skateboards as the ball is thrown and caught? 27

4 5.3 How Can You Find the Center of Mass of an Object? 6) Finding the center of mass: Stack one wooden block on top of a second block. Slide the top block so that it is not directly over the bottom block. a) How far can the top block overhang the bottom block before it falls? b) How does the distance the top block can overhang relate to its center of mass? c) Use the gravity set to find the center of mass of the irregularly shaped brown board. Before you begin, attach a piece of paper to the board with tape. Draw a diagram showing the center of mass and how you found it. d) Adapt the method you used in part b) to find the center of mass of a C clamp. (Hint: pieces of string are useful.) Explain what you did. Draw a diagram showing the center of mass of the C clamp. e) Group Discussion Question: On your table is a wooden figure of a man who balances on a wooden block. Where is the center of mass of this figure? 28

5 Name Section Period 5 Exercises: Newton s Laws of Motion Write answers to the questions below. Show your mathematical steps and the units of the quantities. This sheet with your answers should be turned in at the beginning of Period Understanding the fundamental forces: Which of the fundamental forces is responsible for the situations described below? a) a leaf falls from a tree and comes to rest on the ground below b) protons and neutrons are bound together in an atomic nucleus c) uranium nuclei split apart in a nuclear reactor d) atoms of gold are bound together to form a gold ring 2. Understanding Newton s laws: Which of Newton s laws of motion apply to the situations described below? Explain why each law applies. a) jumping on a trampoline causes the jumper to rise into the air b) a bowling ball is released and travels in a straight path down the bowling alley c) a runner exerts more force as she accelerates when she approaches the finish line of a race 3. Understanding center of mass: a) A Buckeye fan carved the letters shown below out of wood. On each letter, draw an X to show the approximate location of the center of mass. b) How should the Buckeye fan arrange the letters? 29

6 30 8/8/12