Force Pairs
Force Pairs - Related Videos
04:01
VSEPR Theory and the Effect of Lone Pairs
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2020
Effect of Lone Pairs of Electrons on Molecule Geometry It is important to note that electron-pair geometry around a central atom is not the same thing as its molecular structure. Molecular structure describes the location of the atoms, not the electrons. The geometry that includes all electron pairs is the electron-pair geometry. The electron-pair geometries describe all regions where electrons are located, bonds as well as lone pairs. The structure that includes only the placement of the...
02:27
DNA Base Pairing
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2020
Erwin Chargaff’s rules on DNA equivalence paved the way for the discovery of base pairing in DNA. Chargaff’s rules state that in a double-stranded DNA molecule, the amount of adenine (A) is equal to the amount of thymine (T); the amount of guanine (G) is equal to the amount of cytosine (C); and the sum of purines, A and G, is equal to the sum of pyrimidines, C and T (i.e., A+G = C+T). Later work by Watson and Crick revealed that in double-stranded DNA, A always forms two hydrogen bonds...
01:17
Sign Test for Matched Pairs
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2025
The sign test for matched pairs offers a robust method for comparing two paired samples, often for the effects of an intervention in one of them. This method is very useful in situations where the underlying distribution of the data is unknown. The test compares two related samples—often pre- and post-treatment measurements on the same subjects—to determine if there are significant differences in their median values. To conduct the sign test, we first calculate the differences in value between...
11:13
Identification of Kinase-substrate Pairs Using High Throughput Screening
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Cited by 1 •
2015
Protein phosphorylation is a central feature of how cells interpret and respond to information in their extracellular milieu. Here, we present a high throughput screening protocol using kinases purified from mammalian cells to rapidly identify kinases that phosphorylate a substrate(s) of interest.
06:45
Force Spectroscopy of Single Protein Molecules Using an Atomic Force Microscope
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Cited by 4 •
2019
We describe the detailed procedures and strategies to measure the mechanical properties and mechanical unfolding pathways of single protein molecules using an atomic force microscope. We also show representative results as a reference for selection and justification of good single protein molecule recordings.
FAQs
Force-pair forces do not cancel in a single free-body diagram because they act on different objects. A diagram for object A includes the force exerted on A, whereas the equal-and-opposite force exerted by A belongs on object B’s diagram. Keeping those diagrams separate prevents an interaction from being mistaken for zero net force on either object.
Equal force magnitudes do not require equal accelerations. Newton’s third-law relationship compares the interaction forces on the two objects, while the objects may have different masses and respond differently. This distinction is especially important in collisions or other interactions where the force pair remains matched even though the observed motions are not.
The two forces arise simultaneously, so neither should be treated as the original force followed later by a reaction. To identify the pair, name both interacting objects and ask what force each exerts on the other. This approach links the two forces to one interaction and helps distinguish them from unrelated forces acting on either object.
In contact situations, the support interaction must be considered on both sides. If one object supports or pushes another, the other object exerts a corresponding force back; these two forces form the pair, even though each belongs to a different object. Recognizing both sides clarifies contact-force analysis and prevents placing both forces on one diagram.
To use force pairs in a free-body analysis, first select one object, then list the interactions involving that object. Draw only the forces acting on it, and identify the counterpart force on the other object separately. Repeat for the second object when needed. This procedure keeps object ownership clear and makes the motion analysis consistent.
Walking illustrates how an interaction produces propulsion. The foot and the ground exert forces on each other, forming a force pair rather than two forces acting on the same body. Examining the force on the person separately from the force on the ground shows how force-pair reasoning connects contact interactions with forward movement.
In a collision, each object experiences the force associated with the other object’s interaction, so the forces must be analyzed on separate bodies. The magnitudes remain equal and directions opposite, while the objects can have different accelerations. Force-pair analysis therefore helps interpret collision outcomes without assuming that both objects undergo identical motion.