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Click here to enter. Click a menu option to view more details Starters Main Courses Desserts Click on the coffee cup to return when Navigating For Vocabulary.

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Presentation on theme: "Click here to enter. Click a menu option to view more details Starters Main Courses Desserts Click on the coffee cup to return when Navigating For Vocabulary."— Presentation transcript:

1 Click here to enter

2 Click a menu option to view more details Starters Main Courses Desserts Click on the coffee cup to return when Navigating For Vocabulary Subject Related Content and tutorials For drill and practice applet

3 Please make your choice from the following selections Click on the document below to see Essential vocabulary for unit 1

4 Please make your choice from the following selections Identifying Forces Solving Problems involving Constant Velocity Solving Problems involving Constant Acceleration

5 Please make your choice from the following selections Block pulled at a constant speed problems Incline Plane Problems Elevator Problems

6

7 Choose from the following options Block Pulled at a constant velocity with NO vectors Block Pulled at a constant acceleration with vectors Block Pulled at a constant velocity with vectors Block Pulled at a constant acceleration with NO vectors

8 60 Degrees ProblemSolution Block Pulled at a Constant Velocity Vectors A block with a mass of 150kg is pulled to the right with a force of 200N at an angle of 60 degrees above the horizontal. If the block has a constant velocity of 9 meters per second, determine the weight of the block, the normal force acting on the block, and the force of friction acting on the block 150 kg -100 N 1297 N 1470 N 200 N 1. To begin click the ‘problem’ button 2. When finished, hit ‘solution’ to see the answer 3. Hit ‘problem’ again to get a new problem 4. Hit the Back button to go back to the type of problem menu 5. Hit the coffee cup to return to the main menu

9 Problem Solution A 60kg person is riding in the elevator depicted below. What is the apparent weight of the rider while the elevator is accelerating downwards with a constant acceleration of 3 meters per second squared? 1. To begin click the ‘problem’ button 2. Hit ‘Free-Body Diagram’ to view the Free-Body diagram for this problem 3. Select F net equation to view the equation used to solve the problem 4. When finished, hit ‘solution’ to see the answer 5. Hit ‘problem’ again to get a new problem 6. Hit the coffee cup to return to the previous menu Free-Body Diagram F net Equation Apparent Weight=

10 Problem Solution A 430kg block is at rest on a ramp with an incline of 30 degrees. Determine the acceleration of the block if the coefficient of static friction is 1.22 and the coefficient of kinetic friction is To begin click the ‘problem’ button 2. Hit ‘Free-Body Diagram’ to view the Free-Body diagram for this problem 3. Select F net equation to view the equation used to solve the problem 4. When finished, hit ‘solution’ to see the answer 5. Hit ‘problem’ again to get a new problem 6. Hit the coffee cup to return to the previous menu Free-Body Diagram 430kg F┴F┴ FgFg F net Equation Acceleration= 0 meters per second squared F Vertical F net Horizontal F net 30 Degrees F gy F gx

11 “The sources of Forces”

12 Identifying Forces Objective: To recognize what are the sources of forces To be able to for any given object and situation, correctly identify what forces are acting.

13 Identifying Forces There are three sources to consider when thinking about what forces are acting on an object. 1. First consider any gravitational forces 2. Second ask yourself what is in contact with the object 3. Finally, are there any frictional forces to consider

14 Identifying Forces(Gravity) Gravity Gravitational Forces exist if the object is located in a gravitational field. For our purposes at this point, all objects on the earth are subject to gravity. One note about gravity, it behaves differently then all of the other forces we are studying. It can act without contact The symbol for the force of gravity is F g

15 Identifying Forces(Gravity) If gravity is present it always pulls an object straight down. It never acts at an angle. FgFg FgFg FgFg FgFg FgFg

16 Identifying Forces(Gravity) The force of gravity is called the weight of an object. When using the word weight in physics, you are referring to the downward pull on that object caused by the force of gravity. Weight and mass are NOT the same thing!!!!!!! The reason this is confusing is because mass and weight are related concepts. The more mass something has the more it weighs. It is important to understand the difference in terminology and what is meant by each word. Remember physics vocabulary is specific and we have specific words for different things to eliminate vagueness. WeightMass The downward pull of gravity on the object The amount of matter an object possess The value of the weight fluctuates as the strength of the gravitational pull changes The value of an objects mass doesn’t change based on gravitational changes.

17 Identifying Forces (Contact) Contact Forces are caused by anything in contact with the object. They are a result of Newton’s third law. They always act in the direction opposite the location of the object. As a result of Newton’s Third law, all exchanged contact forces between two objects are equal and opposite. The symbol for a contact for is always F with a subscript letter representing what is in contact

18 Identifying Forces (Contact) The symbol for a contact for is always F with a subscript letter representing what is in contact. The subscript is up to you but it should make sense. Sometimes a subscript of a few letters or even a whole word is used for clarification. The table below includes a few example contact forces and the symbol that is frequently used. Contact ForceSymbol Air ResistanceFaFa TableFtFt RopeFrFr GroundF gr

19 Identifying Forces (Contact) When identifying contact forces, ask yourself how many objects are in contact. For every object in contact, add one contact force F ground F Air F road F rope

20 Identifying Forces (Contact) Observe the use of Newton’s 3 rd Law with the pictures of the car driving and the jets flying. In both cases the forward motion is a result of contact between them and something else. F ground F Air F road F rope

21 Identifying Forces (Contact) Observe the use of Newton’s 3 rd Law with the pictures of the car driving and the jets flying. In both cases the forward motion is a result of contact between them and something else. F ground F Air F road

22 Identifying Forces (Contact) For the car, the forward force is caused by the car’s tires gripping the road and pushing the road backwards. As a result of Newton’s 3 rd law, the road pushes the car forward with equal force. It is the road that pushes the car forward. F ground F Air F road

23 Identifying Forces (Contact) For the jet, the forward force is caused by the air the jet engines are pushing backwards as exhaust. As a result of Newton’s 3 rd law, the air pushes the jets forward with equal force. This is similar to the car. F ground F Air F road

24 Identifying Forces (Contact) The Normal Force In physics, the contact interaction with a surface is an import concept. Several additional concepts are linked to this interaction. Because of this importance, this contact force is given a special name. The Normal Force. The symbol for the Normal Force is F ┴ Normal Force can be identified either with a subscript identifying the object or with the perpendicular subscript.

25 Identifying Forces (Contact) F Air F road So either label it this way F table F ground

26 Identifying Forces (Contact) F┴F┴ F Air F road Or label it this way F┴F┴ F┴F┴

27 Identifying Forces (Friction) Frictional Forces exist if the following two conditions are true 1. The object is in contact with a surface. 2. The object is either moving or attempting to move. Frictional Forces always act against motion. Frictional Forces are designated F F

28 Identifying Forces (Friction) There is a frictional force present here because Jimmy Rollins is both in contact with a surface(the ground) and is moving. F

29 Identifying Forces (Friction) Once he stops moving, the frictional force will disappear until he attempts to move again F

30 Identifying Forces (Friction) There is no frictional force acting on these blocking sleds. Although they are in contact with the ground, they are stationary and not attempting to move.

31 Identifying Forces (Friction) Once the football players start pushing the sled, there is a frictional force. Although the sled depicted here is stationary, it is attempting to move. You determine if an object is attempting to move by asking yourself, if I eliminate friction, would the object accelerate. If so, then it is attempting to move. F

32 Identifying Forces (Friction) In the is case, since the football players are pushing the sled left, without friction it would accelerate left. Therefore there is friction F

33 Identifying Forces (Summary) There are three sources of forces 1. Gravity 2. Contact 3. Friction When constructing a Free-body diagram consider each category and think about if any of these forces are present.

34 Identifying Forces (Summary) Click here for answer? What forces are acting on the chemistry book?

35 Identifying Forces (Summary) Click here for answer? What forces are acting on the chemistry book? FgFg F Calculas F Psychology Book

36 Identifying Forces Click here to repeat the tutorial Click here to the main course menu Or click the mug to return to the main menu

37 Save for Later As the football players push harder the sled will begin to slide. The force of friction has a max value. It will increase in strength up to that point.


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