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F W =1000N

A 100kg wooden box is standing on a wooden floor. You push the box with a force of 100N to the right. The box does not move. Draw a complete free body diagram of the box and label all forces. F N =1000N. F=100N. F W =1000N. F N =1000N. F=100N. F fr. =100N. F W =1000N. F N =1000N. F=200N.

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F W =1000N

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  1. A 100kg wooden box is standing on a wooden floor. You push the box with a force of 100N to the right. The box does not move. Draw a complete free body diagram of the box and label all forces.

  2. FN=1000N F=100N FW=1000N

  3. FN=1000N F=100N Ffr.=100N FW=1000N

  4. FN=1000N F=200N FW=1000N

  5. FN=1000N Ffr.=200N F=200N FW=1000N

  6. FN=1000N F=300N FW=1000N

  7. FN=1000N Ffr.=300N F=300N FW=1000N

  8. FN=1000N Maximum Ffr.= ? Which force will make the box accelerate? FW=1000N

  9. Static Friction, ƒs • Static friction acts to keep the object from moving • If F increases, so does ƒs • If F decreases, so does ƒs • Static friction has a maximum: ƒs µs FN µs….coefficient of static friction

  10. More About Friction • Friction is proportional to the normal force • The coefficient of friction (µ) depends on the surfaces in contact • The direction of the frictional force is opposite the direction of the applied force • The coefficients of friction are nearly independent of the area of contact

  11. FN=1000N Which force will make the box accelerate? Maximum Ffr.= μ·FN FW=1000N

  12. FN=1000N Which force will make the box accelerate? Maximum Ffr.= μ·FN Maximum Ffr.= 0.42·1000N FW=1000N

  13. FN=1000N Which force will make the box accelerate? Maximum Ffr.= μ·FN Maximum Ffr.= 0.42·1000N Maximum Ffr.= 420N FW=1000N

  14. FN=1000N Maximum Ffr.= 420N Which force will make the box accelerate? – Any force that is larger than 420N. FW=1000N

  15. FN=1000N Fnet= 80N a=0.8m/s2 Maximum Ffr.= 420N F=500N FW=1000N

  16. When a 12-newton horizontal force is applied to a box on a horizontal tabletop, the box remains at rest. What is the force of static friction acting on the box? • According to your reference table, Approximate Coefficents of Friction, what is the minimum horizontal force needed to start a 300. N steel block on a steel table in motion? • According to your reference table, Approximate Coefficents of Friction, what is the minimum horizontal force needed to start a 300. kilogram steel block on a steel table in motion? • Jim wishes to push a 100. N wood crate across a wood floor. According to your table, Approximate Coefficents of Friction, what is the minimum horizontal force that would be required to start the crate moving? • According to your table, Approximate Coefficents of Friction, which road surface would offer the greatest traction for the rubber tires of a 1000kg car? Which force would be required to make the car accelerate on each surface? • dry concrete • wet concrete • dry asphalt • wet asphalt • A 100kg wooden box is at rest on a wooden floor. How much force is necessary to make the box accelerate? • A 100kg wooden box is at rest on a wooden floor. Your friend is pressing the box straight downwards with a force of 500N. How much force is necessary to make the box accelerate? • A 100kg wooden box is at rest on a wooden floor. Your friend is lifting the box straight upwards with a force of 500N. How much force is necessary to make the box accelerate?

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