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183_notes:model_of_solids [2015/09/19 11:27] – [Tension] caballero | 183_notes:model_of_solids [2021/03/13 19:28] – [Tension] stumptyl | ||
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- | ===== Matter | + | Section 4.1, 4.2 and 4.3 in Matter |
- | Until now, you have read (primarily) about forces that result from the gravitational interaction in both its [[183_notes: | + | ===== Matter & Models |
+ | Until now, you have read (primarily) about forces that result from the gravitational interaction in both its [[183_notes: | ||
+ | ** | ||
==== Lecture Video ==== | ==== Lecture Video ==== | ||
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All matter is made up of atoms, which (as you know) are in turn made up of a dense positively charge nucleus (with a $\sim1\times10^{-15}m$ radius) and a sparse, negatively charged electron cloud (with a $\sim1\times10^{-10}m$ radius). The interaction between atoms is due primarily to the charges in the atoms. We observe that when two atoms are near each other, the long range electrical forces cause them to attract, but only up to a point. When atoms are pushed too close together, they begin to repel each other. | All matter is made up of atoms, which (as you know) are in turn made up of a dense positively charge nucleus (with a $\sim1\times10^{-15}m$ radius) and a sparse, negatively charged electron cloud (with a $\sim1\times10^{-10}m$ radius). The interaction between atoms is due primarily to the charges in the atoms. We observe that when two atoms are near each other, the long range electrical forces cause them to attract, but only up to a point. When atoms are pushed too close together, they begin to repel each other. | ||
- | [{{ 183_notes:mi3e_04-003.png? | + | [{{ 183_notes:horizontal_springsystems_compression.png? |
These observations are not unlike those we observe with two ends of a spring (Figure to the right). Pulling the ends apart (past the springs relaxed length) stretches the spring, which results in a force by the spring " | These observations are not unlike those we observe with two ends of a spring (Figure to the right). Pulling the ends apart (past the springs relaxed length) stretches the spring, which results in a force by the spring " | ||
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*/ | */ | ||
- | Using the ball and springs to model the physical characteristics of solids might seem artificial for a number of reasons including that atoms do not have well defined radii. Moreover, it is typically the case that solid materials are made of multiple elements, which implies that the " | + | Using the ball and springs to model the physical characteristics of solids might seem artificial for a number of reasons including that atoms do not have well defined radii. Moreover, it is typically the case that solid materials are made of multiple elements, which implies that the " |
==== Tension ==== | ==== Tension ==== | ||
- | [{{ 183_notes:mi3e_04-008.png? | + | [{{ 183_notes:phy_freebody_3.png? |
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[{{ 183_notes: | [{{ 183_notes: | ||
- | Consider a very thin wire that is one atom thick. In this case, you can observe what happens to each bond in the wire when a heavy ball is attached to the end of the wire (Figure to the left). In this case, each bond is " | + | Consider a very thin wire that is one atom thick. In this case, you can observe what happens to each bond in the wire when a heavy ball is attached to the end of the wire (Figure to the left). |
In a real material, the upper bonds stretch the most because they support the ball attached to the end along with all the atoms below that bond. The lower bonds stretch the least because they have fewer atoms below them to support. Atoms have mass, and each atom is supporting the weight below itself including the attached ball. | In a real material, the upper bonds stretch the most because they support the ball attached to the end along with all the atoms below that bond. The lower bonds stretch the least because they have fewer atoms below them to support. Atoms have mass, and each atom is supporting the weight below itself including the attached ball. | ||
The model that we have proposed (where each bond stretches equal amounts) requires that the atoms have no mass; this leads to the " | The model that we have proposed (where each bond stretches equal amounts) requires that the atoms have no mass; this leads to the " |