The document discusses the forces acting on an object placed on an incline. It explains that the gravitational force always points straight down and does not change in magnitude, while the normal force points perpendicular to the surface and decreases as the incline angle increases. On an incline, the gravitational force can be resolved into components that try to press the object into the surface and slide it down the incline. The normal force opposes only the pressing component, not the entire gravitational force. Friction also acts on inclined surfaces and opposes the sliding component.

1. Forces on an incline

2. The Gravitational forceThe gravitational force on an object always points straight down.And maintains a constant magnitude.FgFgFgFgFgFg

3. The Normal ForceThe normal force on an object always points perpendicular (normal to) the surface of contact.And decreases in magnitudeas the inclines angle increases.FN = 0NFNFNFNFN

4. Why does the Normal Force change, but gravity doesn’t?The Gravitational Force on the object is created by the mass of the object and the mass of the Earth itself. The angle of the incline has nothing to do with the Gravitational Force.The Normal Force, however, is a reactionary force from the incline’s surface on the object. As the object press more on the surface the normal force increases. If the pressing for decreases, so does the normal force.Basically the Gravitational Force wants the object to fall straight down, but the incline’s surface gets in the way, and a Normal Force is produced. The strength of the Normal Force depends on how well the incline can oppose the Gravitational Force .

5. Getting a visual.On a horizontal surface the Normal Force (which is ALWAYS 90O) from the surface directly opposes the Gravitational Force.And if the object is not being accelerated then it is in equilibrium, and so….The object in this case can never be in equilibrium.Fup + Fdown = 0 NFup + Fdown = maFgFgFN + Fg = 0 NFN = - FgThis makes sense, the object is falling.On a vertical surface there would be no Normal Force (which is ALWAYS 90O) from the surface because the object is not pressing on the surface the surface would not create a reactionary force.FN0 N + Fg = mamag = ma ag = a

6. If the object is placed on an incline who has an angle between 0O and 90O, then the Normal Force opposes a component of the Gravitational Force, not all of it.FNFgIn this case the Gravitational Force is trying to do two things…FpressPress the object against the surface of the incline (Fpress)2) Slide the object along the surface of the incline (Fslide)FslideFslideSo we can often think of the F.D.B. for an object on an incline as this.q

7. YY’X’FNqFgXqq

8. Y’X’FNFgFpressFslide = Fg*SinqFslideqFpress = Fg*CosqFN = - Fpress

9. FNFgFNFslide = Fg*SinqFpress = Fg*Cosqqq

10. The Friction ForceVVIf the object is in motion the Kinetic Friction Force on an object always points along the surface of contact, but in the opposite direction of object’s motion if it is moving (Kinetic Friction), and if the object is at rest then friction (Static Friction) opposes the direction that the object is “trying” to move in.FrickFrick

11. Which way will friction go, and what type is it?VV10 kg10 kgFrickFrickFricsFricsRestingResting

12. Forces of a rough inclineThe force on a rough incline are the same as a smooth, with the addition of friction.The gravitational force on the object is still trying to do two things, so we will still work with it’s components.Now we can sayFfrictionFNFgFpressFN = - FpressFgsin(q) + FNm= maFslideFslide + Ffriction = maFgsin(q) +[FgCos(q)]mk = maFgsin(q) +[FgCos(q)]ms = 0 Nq