Forces
Aperçu
Push, pull, stretch, squeeze, turn, stop: forces are behind every change in how an object moves or what shape it is. Understanding forces is the gateway to the whole of mechanics, and it is where Newton's famous ideas about motion begin.
In this lesson you will see how a force can change an object's size and shape, read a load-extension graph and find a spring constant, add forces along a line to get the resultant, and use \(F=ma\) to link force, mass and acceleration. You will also meet the idea that a force at right angles to motion makes an object travel in a circle.
Objectifs
- Know that forces may produce changes in the size and shape of an object
- Sketch, plot and interpret load–extension graphs for an elastic solid and describe the associated experimental procedures
- Determine the resultant of two or more forces acting along the same straight line
- Know that an object either remains at rest or continues in a straight line at constant speed unless acted on by a resultant force
- State that a resultant force may change the velocity of an object by changing its direction of motion or its speed
- [Supplement] Define the spring constant as force per unit extension; recall and use the equation F k = x
- [Supplement] Define and use the term ‘limit of proportionality’ for a load–extension graph and identify this point on the graph (an understanding of the elastic limit is not required)
- [Supplement] Recall and use the equation F = ma and know that the force and the acceleration are in the same direction
- [Supplement] Describe, qualitatively, motion in a circular path due to a force perpendicular to the motion as: (a) speed increases if force increases, with mass and radius constant (b) radius decreases if force increases, with mass and speed constant (c) an increased mass requires an increased force to keep speed and radius constant mv 2 ( F = is not required) r
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Évaluation de la leçon
Félicitations, vous avez terminé la leçon sur Forces. Maintenant que vous avez exploré le concepts et idées clés, il est temps de mettre vos connaissances à lépreuve. Cette section propose une variété de pratiques des questions conçues pour renforcer votre compréhension et vous aider à évaluer votre compréhension de la matière.
Vous rencontrerez un mélange de types de questions, y compris des questions à choix multiple, des questions à réponse courte et des questions de rédaction. Chaque question est soigneusement conçue pour évaluer différents aspects de vos connaissances et de vos compétences en pensée critique.
Utilisez cette section d'évaluation comme une occasion de renforcer votre compréhension du sujet et d'identifier les domaines où vous pourriez avoir besoin d'étudier davantage. Ne soyez pas découragé par les défis que vous rencontrez ; considérez-les plutôt comme des opportunités de croissance et d'amélioration.
- A load of 10 N stretches a spring by 0.05 m. The spring constant is: A. 0.5 N/m B. 2 N/m C. 50 N/m D. 200 N/m Answer: D
- A resultant force of 20 N acts on a 4 kg mass. The acceleration is: A. 0.2 m/s^2 B. 5 m/s^2 C. 24 m/s^2 D. 80 m/s^2 Answer: B
- An object moves at constant velocity. The resultant force on it is: A. equal to its weight B. zero C. equal to friction times two D. increasing Answer: B
- The limit of proportionality on a load-extension graph is where: A. the spring breaks B. extension is zero C. the line stops being straight D. the load is greatest Answer: C
- A force acting at right angles to the motion of an object causes it to: A. speed up B. slow down C. move in a circle D. stop Answer: C
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Livres recommandés
Pour aller plus loin, ressources libres
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Section de manuel
Hooke’s Law: Stress and Strain Revisited
Newton’s first law implies that an object oscillating back and forth is experiencing forces. Without force, the object would move in a straight line at a constant speed rather than oscillate. Consider, for example, plucking a plastic ruler to the left as shown in Figure 16.2 . The deformation of the
"College Physics: Hooke’s Law: Stress and Strain Revisited" by OpenStax, OpenStax, Rice University, licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Source: https://openstax.org/books/college-physics/pages/16-1-hookes-law-stress-and-strain-revisited. Access for free at https://openstax.org/books/college-physics/pages/1-introduction
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Section de manuel
Newton’s First Law of Motion: Inertia
Experience suggests that an object at rest will remain at rest if left alone, and that an object in motion tends to slow down and stop unless some effort is made to keep it moving. What Newton’s first law of motion states, however, is the following: A body at rest remains at rest, or, if in motion,
"College Physics: Newton’s First Law of Motion: Inertia" by OpenStax, OpenStax, Rice University, licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Source: https://openstax.org/books/college-physics/pages/4-2-newtons-first-law-of-motion-inertia. Access for free at https://openstax.org/books/college-physics/pages/1-introduction
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