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Forces and Laws of Motion

Forces and Laws of Motion. Force. Force is the cause of an acceleration, or the change in an objects motion. This means that force can make an object to 1) start moving, 2) stop moving, or 3) change direction. SI unit of Force.

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Forces and Laws of Motion

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  1. Forces and Laws of Motion

  2. Force Force is the cause of an acceleration, or the change in an objects motion. This means that force can make an object to 1) start moving, 2) stop moving, or 3) change direction.

  3. SI unit of Force The SI unit of force is the newton (N). This was named after Sir Isaac Newton. A newton is the amount of force, when acting on 1kg mass, produces an acceleration of 1m/s^2. In other words, N= 1kg x 1m/s^2.

  4. Forces Contact forces is a force that arises from the physical contact of two objects. It is the result of physical contact. Field force is a force that can exist between objects, even in the absence of physical contact between the objects.

  5. Newton's First Law An object at rest remains at rest, and an object in motion continues in motion with constant velocity unless it experiences a net external force. This law is also called Newton’s Law of inertia.

  6. Inertia is the tendency of an object not to accelerate. Newton’s First Law is called the Law of Inertia because if nothing stops an object it will continue in motion. Inertia

  7. Net External Force External Force is a single force acting on an object as result of the interaction between the object and its environment. The net external force is the vector of all the forces acting on a body.

  8. Net External Force To solve for a Net External Force diagram: 1) Define the problem and identify the variables. 2) Select a coordinate system, and apply it to the free-body diagram. 3) Find the x and y components of all vectors. 4) Find the net external force in both the x and y directions. 5) Find the net external force. 6) Evaluate your answer.

  9. Mass and Inertia The mass of an object is directly proportional to the inertia of an object. http://www.glenbrook.k12.il.us/gbssci/phys/Class/newtlaws/u2l1b.html

  10. Equilibrium Objects that are at rest or moving with constant velocity are said to be in equilibrium.

  11. Newton's Second Law The acceleration of an object is directly proportional to the net external force on the object and inversely proportional to the mass of the object. Net external force = mass x acceleration

  12. Example An applied force of 50 N is used to accelerate an object to the right across a frictional surface. The object encounters 10 N of friction. Use the diagram to determine the normal force, the net force, the mass, and the acceleration of the object. (Neglect air resistance.) Answer Fnorm = 80 N; m = 8 kg; Fnet = 40 N, right; a = 5 m/s/s, right Since there is no vertical acceleration, normal force = gravity force. The mass can be found using the equation Fgrav = m * g. The Fnet is the vector sum of all the forces: 80 N, up plus 80 N, down equals 0 N. And 50 N, right plus 10 N, left = 40 N, right. Finally, a = Fnet / m = (40 N) / (8 kg) = 5 m/s/s.

  13. Newton's Third Law If two bodies interact, the magnitude of the force exerted on object 1 by object 2 is equal to the magnitude of the force simultaneously exerted on object 2 by object 1, and these two forces are opposite in direction. OR…. Every action has and equal and opposite reaction.

  14. Weight Weight is the magnitude of the force of gravity acting on an object. Weight is an everyday force that depends on where the object is since weight is dependent on gravity.

  15. Normal Force Normal force is a contact force exerted by on perpendicular to the surface of contact. An example is a table on the floor. The table is at equilibrium because gravity is acting down on it but the normal force of the floor is keeping it stable.

  16. Force of Friction There are two types of friction: 1) Static Friction- the force exerted on a motionless body by its environment to resist an external force. This keeps objects from starting motion. 2) Kinetic Friction- the force exerted on a moving object. This slows down a moving object.

  17. Friction Friction depends on the surface of the objects that are in contact. The rougher the surface the more friction is created. The coefficient of friction is used to show the ratio of the force of friction to the normal force acting between the two objects. Another type of friction is air resistance showing the resistance of fluids, like air and water, on an object. http://www.marsdenshs.qld.edu.au/subjects/science/junior_science/physics/forces.html

  18. THE END

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