# APPLICATIONS OF NEWTON'S LAWS

1K10.30 WALKING SPOOL
1K20.10 FRICTION OF DIFFERENT SURFACES
1K20.30 STATIC VS SLIDING SURFACES
1K20.35 FRICTION ON INCLINED PLANE
1K30.10 BED OF NAILS

 1K10.30 Walking the Spool Pull string at various angles to make spool move forward with rotation, slide without rotating, or move backwards with rotation. Setup Requirements: Off the shelf   Equations: Standard textbook example. The cosine of the angle string makes with horizontal at slide without rotating position = r/R where r is the inner radius.    Safety Issues: none

 1K20.10 Friction of Different Surfaces Pull weights on various surfaces across desktop.Use a spring scale to show how friction depends on roughness of surface. Setup Requirements: Wood, sandpaper,metal and bricks available.   Equations: F= coefficient of friction x normal force   Safety Issues: none

 1K20.30 Static vs. Sliding Friction Using a spring scale and block you can show that static friction is greater than sliding fricton. Coefficient of sliding friction < coefficient of static friction for a given surface. Setup Requirements: Minimal   Equations: Force = coefficient of friction x normal force.   Safety Issues: none

 1K20.35 Friction on Inclined Plane The coefficient of friction can be measured by increasing the angle until object starts to slide. Setup Requirements: Off the shelf   Equations: By splitting the force of gravity into normal component and component along the incline it is found that coefficient of static friction = tangent of angle.   Safety Issues: none

 1K30.10 Bed of Nails (Pressure) Lie down carefully on bed of nails. Spreading your weight out reduces the pressure exerted by any one nail. Compare to putting weight on small heels of high heeled shoes.   Setup Requirements: Off the shelf   Equations: P = F/A   Safety Issues: Holes in you and your clothes.