Hi,everyone I am a HongKonger I study physics in english . Now, I am learning force and motion but I forgot  the concept of the normal reaction and weight , my teacher said I have to read the book to learn it again but I think the most important is `how  to calculate the force ` I think those concept is useless . I want to ask is it useless for know the concept or good for know it? 

Also , I want to ask how to study physics effectively .

（my English is suck ,there may be many grammar mistake,please forgive me)

The term "normal" in this sense means perpendicular. So if you had something sitting on a table, the normal reaction or normal force would be equal to the weight.

If you had the same weight sitting on a slope, it would be less than that. You can break the weight into vectors to determine what it is.

14 minutes ago, J.C.MacSwell said:

The term "normal" in this sense means perpendicular. So if you had something sitting on a table, the normal reaction or normal force would be equal to the weight.

If you had the same weight sitting on a slope, it would be less than that. You can break the weight into vectors to determine what it is.

thank you sir

 

52 minutes ago, J.C.MacSwell said:

You can break the weight into vectors to determine what it is.

And this is really, really important. If not more important than that. It is a simple, basic thing, but really important!

Hello HongKong and welcome.

 

Perhaps these sketches will help?

It is all very well to say perpendicular.

But perpendicular to what?

 

We talk about the normal to a curve or a surface and we mean at right angles to a tangent to that curve or surface.

In the case of the circle in the first diagram the normal is the same line as the radius.

We often talk about an outward normal as I have drawn.

The radius then forms the inward normal.

 

When we come to a plane or a straight line the normal still at right angles to the tangent but we often call the tangent a parallel..

 

If we have a wiggly line the normals at different point point in different directions as shown.
They are not parallel to each other.

 

Finally for the slope or wedge (very common in Physics) ther normals at any to any face or side are parallel to each other.

 

Does this help?

 

 

The last diagram shows also how to clearly distinguish between { horizontal & vertical} and  {normal and tanget}  as pairs.