Does the scalar of Weight (W) = mg all the time?

1. Oct 22, 2015

NYGooner

I have a question in my textbook where I'm given weight of a "penguin in a sled" as 80N but the object is on a 40 degree angle. Is it telling me that on a normal flat surface the weight is 80N so that way to figure out the force of gravity on the x-axis I must divide the W by 9.8 then plug in my m (mass) that I get to find for the force of gravity along the x-axis as: mgsin(theta)? In the solution that a user posted on slader, they said to find mass its W/9.8 even though the object is being used on a incline of 40 degrees?

2. Oct 22, 2015

SteamKing

Staff Emeritus
Doesn't matter what the angle of incline is. The penguin could be climbing up the side of a cliff (angle to the horizontal = 90°), and W = mg for teh penguin.

Think about what is going on. The weight of the penguin (or any object) is produced by the object's attraction to the earth, not some random object nearby. As such, the force vector which we call an object's weight, will have a certain direction, which doesn't change:

Although the weight of an object doesn't change, the same can't be said for any contact forces between the object and an inclined surface, for instance, as you can see in the diagram above.

3. Oct 25, 2015

vanhees71

Just to add: A weight is a force and thus never a scalar!