1. A 100kg wooden box is standing on a wooden floor
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?