# Newton’s Second Law Applied

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Newton’s Second Law Applied
Objective: know: how to calculate force, mass, and acceleration be able to: explain the motion of objects

Daily Quiz 1. What are the three formulas used to calculate Newton’s Second Law? 2. What are the units of measurement used for these calculations? 3. What is the difference between Newton’s Second and First laws?

Newton’s Second Review
The amount of force required to move or stop an object depends on its mass and acceleration Force = mass x acceleration F = ma m = f ÷ a a = f ÷ m

Which will move faster? Rank in order of decreasing acceleration (slowest to fastest): An object with a mass of 1 kg given a force of 1 N An object with a mass of2 kg given a force of 1 N An object with a mass of 2 kg given a force of 2 N An object with a mass of 4 kg given a force of 1 N An object with a mass of 1 kg given a force of 4 N

An object with a mass of 4 kg given a force of 1 N (.25 m/s2)

Steps to Solve 1. Determine the two variables you know
2. Determine the variable you don’t know 3. Decide which formula to use 4. Plug in numbers and do arithmetic (multiply or divide) 5. Solve

Examples 2. If a 1-N net force accelerates a 1-kg mass at 1m/s2, what is the acceleration caused by a net force of 2N on a 2-kg mass? M = 2 kg F = 2N A = ? A = f ÷ m A = 2N ÷ 2 kg A = 1 A = 1m/s2

6. What is the weight on earth of a girl with a mass of 30 kg (acceleration due to gravity on Earth is 9.8 m/s2)? A= 9.8 m/s2 M = 30 kg F = ? F= m x a F = 9.8 m/s2 X 30 kg F = 294 F = 294 N

CALCULATING FORCE WORKSHEET
1. A man hits a golf ball (0.2 kg) which accelerates at a rate of 20 m/s2. What amount of force acted on the ball? 2. You give a shopping cart a shove down the isle. The cart is full of groceries and has a mass of 18 kg. The cart accelerates at a rate of 3 m/s2. How much force did you exert on the cart? 3. The wind pushes a paper cup along the sand at a beach. The cup has a mass of 25 grams ( = ? kg) and accelerates at a rate of 5 m/s2. How much force (in Newtons) is the wind exerting on the cup? 4. You push a friend sitting on a swing. She has a mass of 50 kg and accelerates at a rate of 4 m/s2. Find the force you exerted. 5. How much force would it take to push another, larger friend who has a mass of 70 kg to accelerate at the same rate of 4 m/s2? 6. A worker drops his hammer off the roof of a house. The hammer has a mass of 9 kg, and gravity accelerates it at the usual 9.8 m/s2. How much force does the earth apply to the hammer? 7. A car whose mass is 1000 kg is traveling at a constant speed of 10 m/s. Neglecting any friction, how much force will the engine have to supply to keep going the same speed? (tricky question) (think INERTIA) ( look at the units) Calculate the force in the following problems by using the equation: Force = mass x acceleration F = m x a Be sure to(1) ALWAYS write the equation, (2)plug in the numbers and units, and (3) give the answer with the correct units.

Big Ideas We will create a chart of the big ideas and important things that we have covered so far The most essential things that someone would need to know to be successful in this unit This chart will be left up to help you remember what you have discovered and show how much you now know that you didn’t realize 10 minutes as a group to decide what to put on your poster 5 minutes to post your thoughts

Introduction to Newton’s Third Law
For every action there is an equal but opposite reaction Touch This! Clip Newton’s Third Law Science Theatre

Background Knowledge Acquisition
Read p. 360 – 366 Answer questions 1 – 5 on page 366 Devise a workable definition of Newton’s Third Law and an example Put this information into your graphic organizer from last time (should now be able to complete your entire chart)

Newton’s Third Law For every action there is an equal but opposite reaction When you push on the wall, the wall pushes on you with the same amount of force Impact differs but force is the same

Reflection How do you remember Newton’s Laws How do they relate
How are they different Objective score and rationale