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Transcript
IPS Unit 1.2 Newton’s Second Law Name: _________________ WHAT DO YOU THINK? List three ways you could apply a force onto your partner? Please don’t do it! __________________________________________________ __________________________________________________ __________________________________________________ If Mr. Mellor pushed a tiny freshman as hard as he could, then pushed a BIG senior as hard as he could, how would each move differently during the push? (Don’t worry Mr. Mellor hasn’t pushed a freshman in months!) ________________________________________________________ ________________________________________________________ ________________________________________________________ GOALS FOR THIS ACTIVITY Define force Identify the forces acting on an object. Determine when the forces on an object are either balanced or unbalanced. Compare amounts of acceleration semiquantitatively. Can the same force move a bowling ball and a ping pong ball? Apply Newton’s Second Law of motion to situations in sports activities. Apply the definition of the Newton as a unit of force. Physics Words force (4.3) __________________________________________________________________________________ newton, the unit _________________________________________________________________________________ acceleration (chapter 2) __________________________________________________________________________________ Newton’s Second Law (5.3) __________________________________________________________________________________ mass __________________________________________________________________________________ weight __________________________________________________________________________________ force due to gravity __________________________________________________________________________________ acceleration due to gravity __________________________________________________________________________________ 1 IPS Unit2 5/6/17 FOR YOU TO DO 1. (Teacher demonstration) Hook a force meter to a car and pull it horizontally across the floor. Get to work!!! Make sure that the meter and string are always horizontal. Pull a few times trying to keep the force at a constant 1 newton. A graph will be made showing the amount of force on the y-axis (up and down) and time on the x- axis (left and right). a) What do you observe, see, happening to the cart as it is pulled with a constant force? ______________________________________________________________________________ b) Why is it so difficult to pull at a constant 1 newton of force? ______________________________________________________________________________ Materials: Liquid accelerometer with rubber band and laminate Cart Paper clip String Hanger Various masses One foot of tape 2. So let's try again. We can use gravity to help us out. Get the material listed above and set up as shown. a) By placing masses on the hanger we can let gravity pull the system down (the weight, force of gravity, is what causes the system to move). A mass of 100 grams will apply a force of about 1 newton to the cart system. b) So, add 50 grams to the hanger, making the total hanging mass 100grams. The force of gravity pulling on the system will be 1 newton. 2 IPS Unit2 5/6/17 3. Pull the cart back until the hanger is at the top of the table. Release the cart and look at the liquid accelerometer as the cart is moving. a) Sketch the shape of the water in the liquid accelerometer as it is moving due to the falling mass, not as you stop it. As a class we learned about what a liquid accelerometer tells us about the motion of an object. Using that information answer the following question. b) What does the liquid tell you about the motion of the cart while it is being pulled to the right? __________________________________________________________________________ __________________________________________________________________________ 4. Repeat the process by pulling the cart with a constant force of 2 N by placing another 100 gram mass on the hanger for a total of 200 grams on the hanger. a) Sketch the shape of the water in the liquid accelerometer to the right. b) How is it different from what you observed in "a" when the force was 1 N? ______________________________________________________ c) What does the liquid tell you about the motion of the cart while it is being pulled to the right in this case? Remember to think about what learned about liquid accelerometers. ___________________________________________________________________________ ___________________________________________________________________________ 5. Repeat the whole process by pulling the cart with a constant force of 3 N, which means a total mass of ____________grams will be hanging on the string. a) Sketch the shape of the water in the liquid accelerometer to the right. b) How is it different from what you observed in "b" when the force was 2 N? ______________________________________________________ ______________________________________________________ c) Based on your observations, complete the statement: "The greater the constant, unbalanced force pulling on the cart, the……" ___________________________________________________________________________ ___________________________________________________________________________ 3 IPS Unit2 5/6/17 d) In other words how does the size of the constant, unbalance force affect the motion of an object? __________________________________________________________________________ __________________________________________________________________________ 6 . Repeat step 2b and 2c, using the same amount of constant force, 2 N, to pull the cart of greater and greater mass. a) You should redo it so that the level of the liquid is fresh in your mind. Start off with the cart by itself and a constant force of 2 N (mass of is 200 grams). Sketch the shape of the water in the liquid accelerometer to the right. b) Add a 500-gram mass to your cart and leave the hanging mass alone so that the force is still 2 N. Sketch the shape of the water in the liquid accelerometer. c) How is it different that what you observed in the last one? __________________________________________________________________________ __________________________________________________________________________ d) What does the liquid tell you about the motion of the cart? __________________________________________________________________________ __________________________________________________________________________ e) Repeat the process by adding another 500-gram mass and leaving "B" alone. Record your results in the same manner as you did in 4b . f) What happens to the acceleration of the cart as the cart becomes more and more massive? __________________________________________________________________________ __________________________________________________________________________ 4 IPS Unit2 5/6/17 7. Based on your observations, complete the statement: "If the force acting on the cart is kept constant, when mass is added to the cart, the cart …….." __________________________________________________________________________ In other words if the same force is used to pull the cart, how does increasing the mass of the cart affect the cart's motion? __________________________________________________________________________________ __________________________________________________________________________________ 8. Let’s review: If the pulling force on an object is increased, the acceleration of the object: increases decreases 9. If the pulling force on an object stays the same, but the mass of the object increases, the acceleration of the object: increases decreases 10. As a class read sections 5.1-5.3: pp. 59-61 11. Now your teacher will do three demonstrations. Write an explanation of how each deals with Newton’s 1st law, 2nd law, inertia and mass. a. Parlor trick: __________________________________________________________________ ____________________________________________________________________________ b. Basket balls: _________________________________________________________________ ____________________________________________________________________________ c. Jenga: _______________________________________________________________________ ____________________________________________________________________________ 5 IPS Unit2 5/6/17 Unit 1.2: Newton’s Second Law Reflection Questions Remember to use any new vocabulary from this or previous activities!! 1. How does the size of the unbalanced force acting on the object affect the acceleration of the object? ________________________________________________________________________ ________________________________________________________________________ 2. How does the mass of the object affect its acceleration? ________________________________________________________________________ 3. Why does the mass matter when it comes to the acceleration of an object? ________________________________________________________________________ ________________________________________________________________________ 4. In your own words what does Newton’s 2nd law mean to you? ________________________________________________________________________ ________________________________________________________________________ 5. In other words if the same force is used to pull the cart, how does increasing the mass of the cart affect the cart's acceleration? ________________________________________________________________________ 6. If the pulling force on an object is increased, why does the acceleration increase? ________________________________________________________________________ ________________________________________________________________________ 7. If the pulling force on an object stays the same, and the mass increases why does the acceleration decrease? ________________________________________________________________________ ________________________________________________________________________ 6 IPS Unit2 5/6/17