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Forces in one Dimension

Learn about forces in classical mechanics, the relationship with objects, different types of forces, fundamental forces, free-body diagrams, Newton's laws, units of force, equilibrium, inertia, mass, and Newton's first and second laws.

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Forces in one Dimension

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  1. Forces in one Dimension Chapter 4

  2. Classical Mechanics • Describes the relationship between the ________ of objects in our everyday world and the ______acting on them. • Conditions when Classical Mechanics does not apply: • Very tiny objects (< atomic sizes) • Objects moving near the speed of light

  3. Forces • Commonly imagined as a _____ or _____ on some object. • Forces results from interactions between objects. • _______ quantity (F) • Magnitude • Direction • There are two classes of forces: __________ and __________.

  4. Forces causes objects to _________ the way they _________. • Objects can change their __________. • Objects can ______ or ________. • These changes to motion helps us to _____ the object being acted upon by a force or a series of forces. • This object is also known as the system.

  5. Contact and Field Forces • Contact forces result from ______________between • ___________. • Field forces act between _____________________.

  6. Contact Forces • A contact force exists when an object from the external world ________ a system and thereby exerts a force on it. • The _________ force in the picture to the right is a contact force. • Whenever a force is exerted on an object, the _______ of the object can change, even rigid and inflexible objects. • These changes can be permanent.

  7. Fundamental Forces • These fundamental forces are all _____ forces. • Types: • ______________ force • ______________ force • _____________ force • __________ Decreasing Strength * *

  8. Free-Body Diagrams • These are ___________that help us in _________ involving ________. • They help us to ________ and _______ the forces acting on an object.

  9. Free Body Diagram • Use a free body diagram in order to ________________which we are applying Newton’s laws. • Must _________ all the forces acting on the object of interest. • Choose an appropriate coordinate system. • If the free body diagram is incorrect, the solution will likely be incorrect.

  10. Sample Problem Draw a free-body diagram for the following scenario: A flowerpot falls freely from a window sill. Ignore any forces due to air resistance.

  11. Force and Acceleration • A ______ applied to an object cause the object to experience a _________________, specifically the object ___________. • Acceleration is a vector quantity, thus a force can induce a change in _________ or a _______________. • The applied force and the resulting acceleration are also dependent upon the _________ of the object. • More on this later

  12. Units of Force • SI unit of force is a Newton (N) • US Customary unit of force is a pound (lb) • 1 N = 0.225 lb

  13. Combining Forces • Since forces are __________ they can be added and subtracted like any other vectors. • We will deal with the simple horizontal case now and deal with more complex vector additions in the next chapter. • The ____________is the vector sum of all the vectors acting on an object.

  14. Sample Problem In the figure below, two forces are acting upon the block. Calculate the net force acting on the block. The positive direction is towards the right. -2 N 4 N

  15. Newton’s First Law Explain Newton’s first law of motion in your own words.

  16. Newton’s First Law • An object moves with a _________ that is _______ in magnitude and direction, unless acted on by a _________ net force. • The net force is defined as the _________ sum of all the ________________exerted on the object. If the net force ΣF exerted on an object is zero, the object continues in its original state of motion. That is, if ΣF=0, an object at rest remains at rest and an object moving with some velocity continues with that same velocity.

  17. ΣF = Sum of All External Forces • The net force (ΣF) is the vector sum of all the external forces acting on an object. • External force • Any force that results from the _________ between the ______ and its ____________. C B A ΣF = A + B + C

  18. Newton’s first law of motion in action. F v Thus an object will not change any aspect of its motion unless acted on by external forces. v

  19. Inertia • Is the __________ of an object to _______ in its ______ motion. • In the _________ of a force. • Thought experiment • Hit a golf ball. • Hit a bowling ball with the same force. • The golf ball will travel farther. • Both resist changes in their motion.

  20. Mass • A ________of the ________ of an object to changes in its motion due to a force. • The ______ the mass, the ____ it ________ under the action of a given force. • This definition allows us to relate mass to motion. • In chemistry mass is the amount of matter an object possess. • SI units are kg • Scalar quantity

  21. Equilibrium • An object either _________or moving with a ________ velocity is said to be in equilibrium. • The ___________acting on the object is ______ (since the acceleration is zero.)

  22. Newton’s Second Law • Newton’s 1st law deals with what happens when no net force acts on an object. Newton’s 2nd law deals with what happens when a force does act on an object. The _____________ of an object is _______ proportional to the net force acting on it and _________ proportional to its mass.

  23. Newton’s Second Law • Acceleration is ________ proportional to the net force. a F

  24. Newton’s Second Law • Acceleration is ________ proportional to the net mass. 1 m a

  25. Newton’s Second Law • Newton’s 2nd law stated in equation form is as follows: ΣF = The sum of all the forces acting on an object.

  26. Some Final Notes About Forces • __________ cause changes in motion. • Motion can occur in the ________ of forces. • All the forces acting on an object are added as ________ to find the net force acting on the object. • m is not a force itself

  27. Using Newton’s 2nd Law • Newton’s 2nd law can be used to solve for __________, directly and ________, __________, and ____ indirectly. • Steps for solving Newton’s 2nd law problems: • Read the problem • Draw a free-body diagram • ID all the forces acting on the object • Add the force vectors together • Apply the total force to solve for either mass or acceleration • Apply the kinematics equations to solve for velocity, displacement , or time.

  28. Sample Problem Anudja is holding a pillow, with a mass of 0.30 kg, when Sarah decides she wants it and tries to pull it away from Anudja. If Sarah pulls horizontally on the pillow with a force of 10.0 N and Anudja pulls with a horizontal force of 11.0 N, what is the horizontal acceleration of the pillow.

  29. Gravitational Force • ________________between any two objects. • This is the weakest of the field force, especially when we are talking about the ___________ particles. • This force can be fairly strong when discussing ____________ objects. Fg Fg

  30. Gravitational Force • Expressed by Newton’s Law of Universal Gravitation: • Every particle in the Universe ________ every other particle with a ________ that is ________ proportional to the _______of the _________ between them.

  31. Weight • The magnitude of the gravitational force acting on an object of mass m near the Earth’s surface is called the _______ w of the object. • w = m • g is a special case of Newton’s Second Law • g is the acceleration due to gravity • g can also be found from the Law of Universal Gravitation.

  32. More about weight • Weight is not an ______________of an object. • Mass is an inherent property. • Weight depends upon _________. • Weight varies with the _________ from the Earth’s surface. • g _________ with ________ distance from the Earth’s surface. • The equation for weight derived above can be used to calculate the acceleration on an object falling at the surface of any massive object if the radius of the more massive object is known.

  33. Drag Force • When an object moves through any kind of _____ (air, water, etc.) the fluid exerts a __________on the moving object in the direction _______ to its motion. • The drag force is dependent on the ______ of the object, the ________ of the object, and the _______ of the fluid that the object is moving through.

  34. Terminal Velocity • This occurs when an object is accelerating due to ________. • During free fall the object experiences two forces: ______ and ____________. • _______ a falling object the force of gravity is greater than the air drag. • As the falling object picks up speed, the upward drag force then ______ the downward gravitational force. • The constant velocity that is reached at this point is known as the ________________.

  35. Interacting Forces • Forces always come in ________. • These force pairs are known as _________ pairs. • These pairs will be _____ in _______ but _______ in __________. • __________________ summarizes the relationship between two forces.

  36. Newton’s Third Law • _______________is premised on the fact that forces in nature do not act alone. • Forces always act in ___________ pairs. • These opposing forces are always ________ in magnitude.

  37. Newton’s Third Law • Therefore, single isolated forces _____________. If object 1 and object 2 interact, the force exerted by object 1 on object 2 is equal in magnitude but opposite in direction to the force exerted by object 2 on object 1.

  38. Newton’s Third Law: Identifying the Interacting Pairs • F12 may be called the ______ force and F21 the ________ force. • Actually, either force can be the action or the reaction force. • The action and reaction forces act on __________ objects.

  39. Forces Acting on an Object • Newton’s Law uses the forces acting onan object. • are acting on the object. • are acting on other objects.

  40. Sample Problem Identify the interacting pairs in the figure below.

  41. Some Action-Reaction Pairs • is the _________, the force the table exerts on the TV. • is always ____________ to the surface. • is the reaction – the TV on the table.

  42. Normal Forces (n) • These are forces that are always directed _________ and run __________ to a surface of an object and act upon the object. • n ________ the ________ of the object it is directed towards. • The __________ may vary depending upon the object exerting the force. • n = Fg so long as the object exerting the normal force can _________ the weight of the object resting upon it.

  43. Applications of Newton’s Laws • Assumptions • Objects behave as particles. • Can ignore rotational motion (for now) • Masses of strings or ropes are negligible. • Interested only in the forces acting on the object. • Can neglect reaction forces

  44. More Assumptions – Ropes • Ignore any ______________of the rope. • Ignore the ______ of the rope. • The magnitude of the force exerted along the rope is called the ___________. • The tension is the _______ at all points in the rope.

  45. Solving Newton’s Second Law Problems • Read the problem at least once. • Draw a picture of the system. • Identify the object of primary interest • Choose an appropriate coordinate system • Draw a free-body diagram • Indicate forces with arrows • Label each force. • Use labels that bring to mind the physical quantity involved. • Use the kinematic equations when needed. • Apply Newton’s Second Law • The x- and y-components should be taken from the vector equation and written separately. • Solve for the unknown(s)

  46. Sample Problem A 50.0 kg bucket is being lifted by a rope. The rope will not break if the tension is 525 N or less. The bucket started from rest, and after being lifted 3.0 m, it is moving at 3.0 m/s. If the acceleration is constant, is the rope in danger of breaking?

  47. The Laws of Motion The End Chapter 4

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