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Foundation Science Presentation 2

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Forces and Newton's first law

Forces and Newton's first law

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• 1. Today’s Objectives-Learn what a force is-Learn what balanced and unbalanced forces are-Learn Newton’s first law of motion
• 2. What is a Force?A force is a push or pull on an objectA force has a size AND a directionIs a force a scalar or vector quantity?Examples of forces:-Pushing your book across a table-Pushing a boxA force must have adirection, so it is a vector quantity
• 3. The Units of ForceForce is measured in NewtonsNewton is abbreviated “N”Newton (N) = kg x m/s2m/s2 is accelerationSo, one Newton is the amount of force that will accelerate a 1 kgobject at 1m/s2 Force is mass x acceleration f ma
• 4. Vector NotationIs force a scalar or vector?Vector.We label vector quantities by putting an arrow over the letter.For example, force = mass x acceleration…….  f ma Arrow indicates that it is a vector quantity
• 5. Forces are shown as arrows, or vectorsThe longer the arrow (vector), the greater the forceThe direction of the arrow shows you the direction of the force 10 N east N 5 N east Vectors
• 6. Adding ForcesMore than one force on an object will be added.So, if two people are pushing something east, one pushing with5N, the other with 10N, what will be the net force on the box? 10 N east + 5 N east 15 N east = net force
• 7. Balanced and Unbalances ForcesBalanced forces: when 2 forces cancel each other (no movement)  10 N force east 10 N force west f 10 N 10 N 0NThere is no movement in balanced forcesExample of a balanced force??
• 8. Balanced and Unbalances ForcesUnbalanced forces: forces that do not cancel (create movement) 10 N force east 15 N force west 5 N west  f 15 N 10 N 5 NwestObject would move to the west in this exampleExample of an unbalanced force??
• 9. Newton’s First Law of MotionNewton’s first law – an object in motion will stay in motion; anobject at rest will stay at restNewton’s first law explains why the motion of objects change.Inertia is an object’s resistance to stop moving or start movingExamples of inertia:-A person flies forward when a car stops-A person flying over bike handlebarsInertia in action…..
• 10. Complete Questions in Notebook1. What is a force?2. Is force a scalar or vector quantity?3. Are you exerting a force on the ground right now?4. What are the units of force? 5. What does the arrow indicate in the following equation? f ma6. How much acceleration will there be when a 1 Newton force pushes a 1 kilogram object?7. Due to the earth’s size, objects accelerate toward the earth at a constant speed of 9.81 m/s2 . If you drop a basketball from an airplane, how fast will it be going after 5 seconds??8. Will a balanced force accelerate an object?9. If an 18-wheel truck weighing 9000kg and accelerating at 2m/s2 east hits a pickup truck weighing 900 kg and accelerating at 21m/s2 west, which way will the 2 trucks travel after the collision, east or west?10. In a car, what is used to stop a person’s inertia during an accident?Write your answers and the questions in your notebook