Y36MVR Second Life inclined plane

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1 Y36MVR Second Life inclined plane Ondřej Bartas, Petr Minařík, Radek Okrajek - Wednesday, 11:00 License: GNU LGPL Inclined plane The inclined plane is one of the original six simple machines; as the name suggests, it is a flat surface whose endpoints are at different heights. By moving an object up an inclined plane rather than completely vertically, the amount of force required is reduced, at the expense of increasing the distance the object must travel. The mechanical advantage of an inclined plane is the ratio of the length of the sloped surface to the height it spans; this may also be expressed as the cosecant of the angle between the plane and the horizontal. Note that due to the conservation of energy, the same amount of mechanical energy is required to lift a given object by a given distance, except for losses from friction, but the inclined plane allows the same work to be done with a smaller force exerted over a greater distance. Calculation of forces acting on an object on an inclined plane N = Normal force that is perpendicular to the plane m = Mass of object g = Acceleration due to gravity θ (theta) = Angle of elevation of the plane, measured from the horizontal f = frictional force of the inclined plane To calculate the forces on an object placed on an inclined plane, consider the three forces acting on it. Air resistance may be neglected for most calculations, except at high speeds. 1. The normal force (N) exerted by the plane onto the body, 2. the force due to gravity (mg - acting vertically downwards) and 3. The frictional force (f) acting parallel to the plane. We can decompose the gravitational force into two vectors, one perpendicular to the plane and one parallel to the plane. Since there is no movement perpendicular to the plane, the component of the

2 gravitational force in this direction (mgcosθ) must be equal and opposite to normal force exerted by the plane, N. If the remaining component of the gravitational force parallel to the surface (mgsinθ) is greater than the static frictional force fs - then the body will slide down the inclined plane with acceleration (gsinθ - fk/m), where fk is the kinetic friction force - otherwise it will remain stationary. When the slope angle (θ) is zero, sinθ is also zero so the body does not move. ( ) Realization in Second Life environment Modeling Creation of model in SL is in basics very similar to other 3D modeling tools, like for example blender or 3D Studio Max. However, as you may expect, it s much less complex. Picture 1: modeling toolbar Creating objects To create an object, you may choose from different basic shapes, like box, sphere, pyramid, hemisphere and much more. There are also more complex objects like tree and grass deployed by Linden Labs.

Picture 2: object selection To create an object, simply select it in the toolbar and by clicking on the ground, place it in the environment.

Basic tools like resizing or rotation are available thru keyboard shortcuts ctrl enables rotation mode and ctrl+shift rotation mode.

Picture 3: Object modification rotate Picture 4: Object modification rotate To precisely adjust the parameters, you may visit Object, which allows you to

3 Picture 2: object selection To create an object, simply select it in the toolbar and by clicking on the ground, place it in the environment. Modifying objects After placing the object, you can easily modify it. Basic tools like resizing or rotation are available thru keyboard shortcuts ctrl enables rotation mode and ctrl+shift rotation mode. Then you can adjust the object by holding left mouse button and moving the mouse on according axes. Picture 3: Object modification rotate Picture 4: Object modification rotate To precisely adjust the parameters, you may visit Object, which allows you to set parameters to specific values. It also allows you to modify object by twisting it, making it hollow, or setting the type of the object. Setting type is very nice feature as it allows you to easily set object to be exactly where you want it or act according to the laws of physics. As for physics, it also allows you to set the material.

Parts of linked objects may be edited using Tools->Edit linked parts command this allows you to select and edit basic parts of object without removing link between the parts.

4 Picture 5: Modify object tab Unfortunately, there are no tools like merge or contract, which would make modeling a lot easier sometimes. This is partially replaced by ability to link objects together to make more complicated objects. This is done using Tools->Link menu or ctrl+l shortcut. Parts of linked objects may be edited using Tools->Edit linked parts command this allows you to select and edit basic parts of object without removing link between the parts. Also sizes of objects are limited, so to make bigger ones (for example ramp for our inclined plane), you can t use one long plane, but you have to link few smaller ones. This is a very problematic part, if you need (like us) to make long flat surface, as even if you try to be as much precise as you can, there will be seems between the objects, causing unwanted behavior. For example when the sphere goes down the ramp, it sometimes bounces. One of the biggest problems with modeling in SL is view. As it is designed as a game, where you are represented by an avatar, also modeling is realized from the view (3 rd person view) of the character. Yes you can, activate view from the eyes of avatar, but this is limited to only looking around. As you have to move character to have different view on scene, you are very often confused or can t easily see the scene to make modeling easier. Also absence of more views (top, left, right, front, bottom, perspective) makes things more complicated. To fly with camera around avatar, you can t use mouse as you would expect (mouse can be used only for zooming as for the view), but you have to use on screen controls. Picture 6: On-screen controls to adjust view

5 Texturing Texturing in Second life is intuitive and easy. You can use your own textures or you can choose texture from large library. To apply texture, you need to go to object edit mode and select Texture. Here you can select texture to use from default library or from your uploaded textures and adjust its properties to fit correctly on the object. To import your own texture follow these steps: Picture 7: Applying textures 1. Go to File -> Upload Image (ctrl + u) 2. Choose your image and upload it 3. Now click on upload. 4. You can find your texture like in first tutorial but not in library, but in you inventory. Unfortunately to upload images you need some Second Life money. Scripting Scripting in second life is difficult especially because of almost no documentation of the language. There are sites like but without real examples of what

6 exactly the script does. Another issue is modification of script no one except author was able to see or modify the script. There is no function documentation, to show what and when each function does. For example there was problem with IISetPos(vector variable), which works only when object is non-physical. Even then, it must be called several times because of limit in object moving (10 meters). Fortunately it s easy to convert non-physical object to physical using llsetstatus(status_physics, TRUE). Physical properties of the object work actually well, considering weight and shape of the object. Second Life also has very good information sources about system (acceleration, physical forces, gravity, ) but also lacking documentation. Communication between objects is realized using channels. Therefore you can have several objects on same channel and control them all at once. Picture 8: Editing scripts in Second Life Team work Team work in SL is also complicated as there were 3 people working on this project, we often run into problems with object sharing, when someone couldn t edit objects created by other user or couldn t perform certain operations on them. Setting privileges was somehow complicated and often without an effect.

To get to the deck, you may use the elevator, which works as you may expect you can call it to your floor using the button and

7 Result Our work lies on a small island, consists of deck from which balls are dispatched with user manual on the board. There are 2 ramps from which the balls are let down. To get to the deck, you may use the elevator, which works as you may expect you can call it to your floor using the button and ride it there sitting in it. There are 4 different types of balls red and green metal, blue rubber and yellow wood. You just need to click on them to dispatch. Picture 9: Whole construction Picture 10: Elevator

8 Picture 11: Inclined plane detail

4.5 Conservative Forces

4 CONSERVATION LAWS 4.5 Conservative Forces Name: 4.5 Conservative Forces In the last activity, you looked at the case of a block sliding down a curved plane, and determined the work done by gravity as