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Do Now for 4/23/13

Do Now for 4/23/13. Take out E78 HW: Complete E78 Analysis Activity 77 and 78 will be checked tomorrow. E78 Force , Acceleration and Mass. Today’s Target: I will be able to see the relationship between the mass of an object, and the force needed to accelerate it. Check HW Go over Part A

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Do Now for 4/23/13

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  1. Do Now for 4/23/13 Take out E78 HW: Complete E78 Analysis Activity 77 and 78 will be checked tomorrow

  2. E78 Force, Acceleration and Mass • Today’s Target: I will be able to see the relationship between the mass of an object, and the force needed to accelerate it. • Check HW • Go over Part A • Complete Part B and C • Complete Analysis 2 through 5

  3. E78 Force, Acceleration and Mass • Speed – The rate a certain distance is traveled. Ex: mph, kph, m/s, cm/s • Acceleration – The rate at which speed is changing. Getting faster or slower. • Ex: Car moving at a constant speed of 60 mph = NO acceleration • A car going from 0 mph to 20 mph in 5 seconds = acceleration of 4 mph/s. • Mass – measured in Kilograms (kg) • Force – measured in Newtons (N)

  4. E78 Force, Acceleration and Mass • Ex: If a car traveling at 8 m/s to the right takes 2 seconds to speed up (accelerate) to 12 m/s in the same direction, what is its acceleration? • Acceleration (a) = Change in speed (m/s)/Time (s) • Acceleration (a) = 12 m/s – 8m/s 2s • Acceleration (a) = 4m/s ÷ 2s = 2m/s/s to the right.

  5. E78 Force, Acceleration and Mass • What is the relationship between the mass of an object and the force it needs to accelerate? • Complete part B and C to find out! • Force (f) = Mass (m) X Acceleration (a) • F= m x a OR F = ma

  6. E78 Force, Acceleration and Mass • F = m x a • m = F/a • a= F/m

  7. E78 Force, Acceleration and Mass • Complete analysis 1 through 5 • 1. Look at your graphed line for “Experiment 1.” • Explain why it does or does not indicate that there is a relationship between force and acceleration. • It does indicate a relationship because in both experiments, as the force increases, so does acceleration. In this case the graph shows that the relationship between force and acceleration is linear because the best fit for the data set is a straight line.

  8. E78 Force, Acceleration and Mass • 2. Compare the two lines, “Experiment 1” and “Experiment 2” on your graph. Identify and explain: • a. any similarities. • The similarities are that both plots show a direct relationship between force and acceleration, both have straight lines that go through the origin, and both have a positive slope. This is a result of graphing the relationship F = ma when the mass is held constant. In this situation, force versus acceleration will always be a straight-line graph that goes through the origin and have a slope equal to the mass.

  9. E78 Force, Acceleration and Mass • b. any differences. • The major difference in the graphs is that the second plot has a steeper slope. The slope on “Experiment 2” is steeper than the slope from “Experiment 1” because the mass is 4 kg in “Experiment 2” and the mass is 2 kg in “Experiment 1.”

  10. E78 Force, Acceleration and Mass • 3. Use your equation for force, mass, and acceleration to find the missing values in the table below.

  11. E78 Force, Acceleration and Mass • 4. In the first activity, Vehicle 2 has greater acceleration than Vehicle 1, but has a less forceful engine. How can this be? Explain in terms of your equation. • Vehicle 2 can have a greater acceleration with less force if it has a lower mass than Vehicle 1. Newton’s equation, F = ma, can be rewritten as a = F/m, which shows that acceleration is the ratio of force to mass. Thus, for an object to obtain a higher acceleration with less force, it must have less mass.

  12. E78 Force, Acceleration and Mass • 5. One newton of force is the same as 1 kg x 1 m/s2. Use your equation to explain why this makes sense. • Since force, measured in newtons, is equal to mass times acceleration, the unit of force, must be equal to the unit of mass (kg) times the unit of acceleration (m/s2), which is known as the compound unit of kg-m/s2.

  13. E78 Force, Acceleration and Mass – Key Points • 1. There is a direct relationship between the force applied to an object and its resulting acceleration. • 2. When an object is subject to a force, there is an inverse relationship between its mass and its resulting acceleration. • 3. Mathematics is important in all aspects of scientific inquiry.

  14. E78 Force, Acceleration and Mass - Vocabulary • 1. m/s2: Unit used to express acceleration; meters per second per second. • 2. Newton (N): The (SI) unit for force; 1 kg x 1 m/s2.

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