The idea here is to draw one-body force diagrams with the mouse. A calculator is not needed since there is no need to calculate an angle or a distance or a trig function. Everything needed for quickly drawing real one-body force diagrams is given on the screen in one place or another.
Solving any example in this series involves three
First, you are given the object's mass times acceleration and asked to use the mouse to draw a vector representing the resultant force on the object. This resultant force is sometimes called "the force on the object," "the total force on the object," "the net force on the object, or "the sum of the forces on the object." They are all the same thing.
Second, you are given the weight of the object and asked to draw a vector representing the non-contact force on the object, the downward force of gravity.
Third, you are asked to look at the physical situation and draw vectors representing the contact forces acting on the object. These are the forces exerted on the object by other objects through points of physical contact. For example, a force might be exerted by a taut rope tied to the object or, if the object is in contact with the earth, by the force with which the earth pushes back on the object to keep the object's weight from causing any further compression or penetration of the earth by the object.
The goal in each example is to properly draw all of the forces acting on the object so that the sum of those forces exactly equals the resultant force you drew from the mass times acceleration.
The reason for starting each example with an object's acceleration is that in every-day life one can often note whether an object is stationary or accelerating and from that gauge the nature of the forces at work on the object. Daily practice in making such observations leads to exciting and useful understandings.
|This area contains a diagram of the physical arrangement and the data for the example.||This tiny area tells you what you must do right now: "read in area to left," "click below," "draw below," whatever.|
|This area displays a list of your correctly
drawn vectors and their components.
|This bigger area is where you draw vectors by holding down the left mouse button while you move the mouse.|
The small upper right area will tell you what to do to get started and for each step. So when you finish a step, look up at this area to see what to do next.
The large lower right area is where you draw vectors. When you have drawn one correctly, you will be told that it is now correct and the vector will appear in component form in the area to the left under the heading "correctly drawn."
The lower left area shows the components of your correctly drawn vectors. If components of a vector are shown in two coordinate systems, both sets of components will be necessary to complete the solution.
How to draw a vector with the mouse: Put the mouse cursor somewhere in the lower right area and push down on the left mouse button and hold it down. A vector will appear with its head at that point and the coordinates of that point will be shown. Simply drag the head of the vector to the right place and then let the mouse button up.
If there is no acceleration (look in the upper left area) then all of the object's acceleration components are zero so all components of the resultant force on the object are zero. If you are asked to draw such a zero force vector, simply click anywhere to get a vector and then drag the vector head to the place where both of the force components are shown as zero.
When beginning an example be sure to notice, in the upper left area, whether the object is said to be accelerating.
You can quit an example at any time and return to the examples menu by following your usual procedure for going back to your browser's previous page (usually by clicking a large left-pointing arrow in your browser's upper left corner).
You can quit the entire program at any time in the usual fashion, namely by clicking the white "X" in the red square in the extreme upper right corner of your browser window.
Here is a "draw 1 force" example:
Here is a "draw 2 forces" example:
Note: When you have drawn both vectors successfully, you will be informed of your success and you will then be asked to click the mouse button to submit your success. However, first look in the lower left box and check that the sum of your two vectors equals your resultant force vector. Then click to reset.
To leave these practice examples, use the Back Button on your browser or simply dismiss this window by clicking the white "X" in the red square in the far upper right corner of the window.