Physical Science 8th grade (1).pdf

# 2 check to see that your scale is calibrated to read

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2. Check to see that your scale is calibrated to read zero when nothing hangs from it. 3. Hang the 50-gram mass on the scale and measure the force of gravity (weight) in newtons. Record your value in the table. 4. Repeat with the 100, 200, and 500-gram masses. 5. Measure the weight of 10 washers, 20 washers, and 30 washers. Use what you learned during this activity to calculate the mass of these groups of washers. Applying your knowledge a. If you know the mass of an object in kilograms, how can you calculate its weight in newtons on Earth? b. If you know the weight of an object in newtons on Earth, how can you calculate its mass in kilograms? c. The three blocks are the same size, but do they have the same weight? Why? Object Mass (kilograms) Force of gravity (newtons) 50-gram mass 100-gram mass 200-gram mass 500-gram mass 10 washers 20 washers 30 washers Chapter 13 Connection

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C HAPTER 13 F ORCES 285 Chapter 13 Assessment Vocabulary Select the correct term to complete the sentences. Section 13.1 1. ____ is the force that resists the motion of objects or surfaces. 2. When a box is being pushed across a floor, ____ acts between the box and the floor. 3. If you stand still on the side of a hill, ____ keeps you from sliding down the hill. Section 13.2 4. The ____ is the combination of all the forces acting on an object. 5. A(n) ____ has both an amount and a direction. 6. The ____ of an object changes due to the gravitational force acting on it. 7. In the metric system, all forces are measured in ____. 8. An object will have the same ____ if it is on Earth, the moon, or any other planet. 9. When a rope is being pulled from both ends, the force acting through it is called ____. 10. The ____ acts perpendicular to the surface of a book resting on a table, and balances the weight of the book. 11. A ____ is a drawing that shows all the forces affecting an object. 12. An object is in ____ when all of the forces on the object balance and there is no net force on the object. Concepts Section 13.1 1. Which has more mass, a 10 N object on the moon, or a 10 N object on Earth? 2. Explain why ice generally has very little friction when it is in contact with other materials. 3. When you put your groceries on a conveyer belt at the supermarket, friction plays a part in how the objects move down the belt. Describe how the friction acts on your food, and why this is the case. 4. Describe the difference between sliding friction and static friction. 5. Explain how friction keeps a nail in place in a block of wood. If you try to pull out the nail, which way does the friction act? Section 13.2 6. For each of the following, tell whether it is a vector. a. 20 N west b. 42°C c. 3:15 pm d. 5 km down e. 20 m/s f. 30 m/s to the right 7. Draw the following vectors on a piece of paper and show the scale you use: a. 20 m/s west b. 3 miles north c. 4 N southeast vector weight friction equilibrium static friction normal force tension newtons net force sliding friction free-body diagram mass
286 C HAPTER 13 F ORCES 8. What four main forces act on an airplane in flight? If the plane accelerates forward, which two forces must be out of balance? To fly on a level path, which two forces must be in

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