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Forces and Newton’s Laws

Forces and Newton’s Laws. Unit 5. A Force is…. A “push” or “pull” Measured in Newtons (N) in the metric Measured in pounds (lbs) in the English system A vector quantity Represented by drawing arrows on a diagram. Mass - Refresher. The amount of matter an object is made up of.

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Forces and Newton’s Laws

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  1. Forces and Newton’s Laws Unit 5

  2. A Force is… • A “push” or “pull” • Measured in Newtons (N) in the metric • Measured in pounds (lbs) in the English system • A vector quantity • Represented by drawing arrows on a diagram

  3. Mass - Refresher • The amount of matter an object is made up of. • Measured in kilograms. • NOT a force.

  4. Weight The force of gravity acting on a mass. Weight always acts down! F = m x a (N) = kg x m/s2 wt = m x g Fg= wt Weight = mass (kg) x acceleration due to gravity ( m/s2 ) Weight is a force…so this is a special case of F=ma and the unit is a Newton. *FYI You must remember that if given only mass and asked to solve for Fg – you must multiply the mass x accel. ( due to gravity ) to have a Force.

  5. Let’s convert your weight in lbsto Newtons. • 1st • What is your weight in lbs? • Use the conversions • 1lb = 0.45 kg • 2nd • Multiply • m x g • 3rd • Compare the difference of • lbs to Newtons • Kinda strange #’s

  6. Rearrange the Force formula to : • Solve for a ? • Units for a = ____ • Solve for m? • Units for m = ____

  7. 2 particular types of forces are: • Balanced forces – equal and opposite • Equilibrium • No Net Force • FNET = 0 • Unbalanced forces – not equal and opposite • There is a Net Force.

  8. Types of Forces • FgWeight - force of gravity( requires m x a) • FNNormal force – surface pushing back ( requires contact between surface ) • FfFriction - resistance force (opposing F – goes in opposite direction of another F ) • Fair Air -resistance force ( also opposing F ) • FApApplied force - force you exert ( person or animal ) • FTenTension - applied through a rope or chain • FNETNet force – total vector sum of all forces

  9. Normal Force (FN) • Defined as the force of a surface pushing back on an object. • Always directed perpendicular to the surface. • This is a contact force. No contact…no normal force. • NOT always equal to weight. See diagrams below. FN Examples: FN Wa l l Table

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