variable Formula S or v SI variable Formula S or v SI 4. How is a Newton defined? What does a Newton equal in pounds?

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1 Newton s Laws 1 1. Define mass variable Formula S or v SI 2. Define inertia, how is inertia related to mass 3. What is a Force? variable Formula S or v SI 4. How is a Newton defined? What does a Newton equal in pounds? 5. What is an action force? How is it identified? 6. What saying will we use to identify the number of action forces on an object? 7. How many action forces are there in the following situations? Draw and label Box sitting on the ground Box being pulled by a rope Box being dropped These are called Free Body Diagrams

2 Newton s Laws 2 8. Identify the special forces and how they are drawn Force Name What is it? Does it have special rules? Weight Normal Force? Tension Friction State Newton s first law (Galileo s law of inertia)? 8. What is meant by a net force? 9. What kind of motion does Newton s first law discuss? 10. What would a vector addition diagram look like for Newton s first law? 11. What is translational equilibrium?

3 Newton s Laws 3 Problem-Solving Strategy Statics The following procedure is recommended for problems involving objects in equilibrium. a. Make a sketch of the situation described in the problem statement. b. Draw a free-body diagram for the isolated object under consideration, and label all external forces acting on it. c. Resolve all forces into x and y components, choosing a convenient coordinate system. d. Use the equations ΣF y = 0 and ΣF y = 0. Keep track of the signs of the various force components. e. Application of step 4 leads to a set of equations with several unknowns. Solve the simultaneous equations for the unknowns in terms of the known quantities. Try These: A 20.0 kg object is hung from the ceiling by a chord. Find the tension in the cord A box is pulled at constant speed along the ground by a rope the makes an angle of 35 0 to the horizontal. What is the frictional force acting on the box? A child holds a sled at rest on a frictionless, 25 0 snowcovered hill. If the sled weighs 77.0 N, find the force exerted on the rope by the child and the force exerted on the sled by the hill. Find the tension in cable 1 and 2

4 Newton s Laws 4 State Newton s second law of motion (the law of acceleration) 12. What type of motion does the second law discuss? 13.What would a vector addition diagram look like for Newton s 2 nd law? Problem-Solving Strategy Dynamics The following procedure is recommended for working problems that involve the application of Newton s second law. 1. Draw a simple, neat diagram of the system. 2. Isolate the object of interest whose motion is being analyzed. Draw a free-body Diagram for this object. When there are multiple objects of interest, draw a separate diagram for each object. 3. Establish convenient coordinate axes for each object, and find the components of the forces along these axes. 4. Apply Newton s second law in the x and y directions for each object. 5. Solve the component equations for the unknowns. Remember that, in order to obtain a complete solution, you must have as many independent equations as you have unknowns. 6. If necessary, use the equations of kinematics(motion with constant acceleration) To find all of the unknowns. Newton s Laws 5

5 Try These A 5.0 kg object is given an upward acceleration of.30 m/s By a rope pulling straight upward. What is the tension in the rope? A constant force acts on a 5.0 kg object and reduces its velocity form 7.0 m/s to 3.0 m/s in 3.0s. What force acts on the object? A 400 g block with an initial speed of 80 cm/s slides along a horizontal tabletop against a friction force of.70 N. How far will it slide before stopping? A 80 kg man standing is standing in an elevator on a bathroom scale. If the elevator is descending with an acceleration of.9 m/s 2, what does the scale read? A 40 kg sled starting from rest slides down a 50 0 frictionless hill. How long does it take to go 40 m? Two masses, M and m, are hung over a massless, frictionless pulley as shown below. If M > m, what is the downward acceleration of mass M? Give your answer in terms of M, m and g

6 Newton s Laws What is the cause of friction? 15. What is the difference between Static friction Kinetic friction 16.What is the coefficient of friction? variable Formula S or v SI CGS BES Try these A 20 kg block sliding across a table top with a speed µ of 5 m/s comes to rest in 3.0s. What is the k between the block and table? The µ s between a box and the flat bed of a truck is.60. What is the maximum acceleration the truck can have along level ground if the box is no to slide?

7 Newton s Laws 7 What is the coefficient of friction between the block and surface? Write your answer in terms of f, m, F, φ A 40 kg crate is pulled over a horizontal surface by 200 N force acting through a rope that makes an angle of 25 0 with the surface. What is the acceleration of the crate if the µ k is.44? State Newton s 3 rd law ( the law of interaction) 17. What is an action force? ( look at question #5) 18. What is a reaction force? 19. What is an pair? 20. Do action reaction pairs happen at the same time? 21. If action reaction pairs are always equal and opposite, how can anything move?

8 Newton s Laws 8 Try these : A box is sitting on the floor. Draw and label all of the action forces. Then in the chart to the right give the cause of all of the action forces. Then identify all of the reaction forces. Finally, draw and label all of the reaction forces. In the picture below who is pulling harder? Show all of the action reaction pairs A horse is pulling a cart down the road. Assume that the connection between horse and cart is level. Draw and label all action reaction forces on the horse and cart Horse Cart

Newton s Laws 9 22. When added what do the action forces tell you? 23. When added what do all of the reaction forces tell you? 24.

9 Newton s Laws When added what do the action forces tell you? 23. When added what do all of the reaction forces tell you? 24. Give all of the action- reaction pairs Lawn Mower 25. Using the ideas gained about Newton s third law explain how a rocket flies. Rocket

Chapter 4. Forces and Newton s Laws of Motion. continued

Chapter 4. Forces and Newton s Laws of Motion. continued Chapter 4 Forces and Newton s Laws of Motion continued 4.9 Static and Kinetic Frictional Forces When an object is in contact with a surface forces can act on the objects. The component of this force acting