2*7 Frictional Force: The Mu of the Shoe

2*7 Frictional Force: The Mu of the Shoe • WDYS? (p210) • . • . • . • WDYT? • Some sports require special shoes because _____. • Different features of a shoe are useful for different sports because _____.

2*7 Investigate (p210) • Brand of shoe = _____ Weight of shoe = _____ • Variables = _____ _____ _____ Surface Type = Table Top • Force of Spring Scale = _____

2*7 Investigate (p210) • When the shoe is being pulled across the table, there are 4 forces acting on it: • _____ • _____ • _____ • _____ • Normal Force = force directed PERPENDICULAR to the surface

2*7 Investigate (p210) • The coefficient of slidingfriction is represented by (μ) = force of friction = ← Normal Force↑ 4. What would happen if you doubled (×2) its weight??? **The value of μ is NOT affected by the weight**

2*7 Investigate (p210) 5. Now, lets do it again on the carpet • Sketch a FBD of the shoe with 4 forces: • μ = • The “rougher” the surface, the _____ the coefficient of friction (μ). The “slicker” the surface, the _____ coefficient of friction (μ). *The value of μ will be DIFFERENT with the surface*

2*7 Physics Talk (p212-214) • Analyzing the Forces Acting on the Shoe • When an object moves at constant velocity the ALL 4 Forces add up to ZERO!!! Constant Velocity = NO Acceleration = Balanced Forces = Net Force is ZERO = Arrows have SAME LENGTH!!!

2*7 Physics Talk (p212-214) HORIZONTALLY • The shoe moved forward at a slow constant velocity, so there is equal and opposite force = FRICTION (←) VERTICALLY • The shoe did NOT move up nor down, therefore the net forces must be BALANCED and EQUAL ZERO • Normal Force (↑) acts perpendicular to the surface; it’s the force of the 2nd object

2*7 Physics Talk (p212-214) 2. Coefficient of Sliding Friction, μ (μ) = force of friction = ← normal force ↑ • (μ) does NOT have units • (μ) expressed in decimals • A change in the SURFACE causes a change in (μ) • the rougher the surface, the greater the (μ) • The smoother the surface, the less the (μ)

2*7 Checking Up (p241) • Because the shoe travels at constant speed, the forces of the spring scale MUST be _____. • The coefficient of friction (μ)has NO UNITS because _____. • The coefficient of friction (μ)is determined by _____.

2*7 TOTD (25pts) • Draw AND Label the 4 forces on an object. • If an object has constant velocity, then the acceleration is _____. • If the forces are balanced, then the arrows are _____. • What is the equal but opposite force to the “pull”? • What is the NAME of the equal but opposite force to gravity?

2*7 PTG (p218)

2*7 Frictional Force: The Mu of the Shoe