Forces And Their Interactions
Aperçu
Hold a magnet a centimetre above a steel paperclip and the clip jumps up to meet it. Nothing touched it. Rest the same clip on a table instead and it sits there, perfectly still, even though gravity is pulling on it the whole time. Two everyday moments, two completely different ways for one object to act on another, and between them they contain most of what this lesson is about.
You will sort every force you meet into the ones that need contact and the ones that reach across a gap, and learn why a force is never something an object simply has. Then you will put a number on gravity itself, work out what you would weigh standing on the Moon without changing your mass by a single gram, and stretch a spring far enough to find the point where it stops behaving itself. This is the first topic of the course, and almost everything that follows leans on it.
Objectifs
- Objects interact by non-contact (field) forces (including gravity, electrostatics, magnetism) and by contact forces (including friction, air resistance, tension and normal contact force).
- Friction is a force between two surfaces, which impedes motion and may result in heating. Air resistance is a form of friction.
- Weight is the force acting on an object due to gravity. The weight of an object depends on the gravitational field strength at the point where the object is. The weight of an object can be calculated using the equation: Weight (N) = mass (kg) × gravitational field strength (N/kg) W=m×g Students will not be expected to know the value of g; it will be given in any examination items.
- A force applied to an elastic object such as a spring will result in the object stretching and storing elastic potential energy.
- For an object behaving elastically, the extension is directly proportional to the force applied, provided that the limit of proportionality is not exceeded. The relationship between the force, F, and the extension, e, is: F=k×e where k is a constant. Required practical: Investigate the relationship between force and extension for a spring.
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Évaluation de la leçon
Félicitations, vous avez terminé la leçon sur Forces And Their Interactions. Maintenant que vous avez exploré le concepts et idées clés, il est temps de mettre vos connaissances à l'épreuve. 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.
- Which of these is a non-contact force? A. Friction B. Tension C. Magnetism D. Normal contact force Answer: C
- A box is pushed across a rough floor. Which statement about the friction acting on the box is correct? A. It acts in the direction the box is moving B. It impedes the motion of the box and may warm the surfaces C. It acts at right angles to the floor D. It acts only after the box has stopped moving Answer: B
- An object has a mass of 4.0 kg. The gravitational field strength is 10 N/kg. What is the weight of the object? A. 0.40 N B. 2.5 N C. 40 N D. 400 N Answer: C
- A force of 12 N stretches a spring by 0.30 m. The spring is behaving elastically. What is the spring constant of the spring? A. 0.025 N/m B. 3.6 N/m C. 40 N/m D. 360 N/m Answer: C
- For a spring behaving elastically, the extension is directly proportional to the force applied only up to a certain force. What is that force called? A. The weight B. The spring constant C. The tension D. The limit of proportionality Answer: D
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Livres recommandés
Pour aller plus loin, ressources libres
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Section de manuel
Normal, Tension, and Other Examples of Forces
Forces are given many names, such as push, pull, thrust, lift, weight, friction, and tension. Traditionally, forces have been grouped into several categories and given names relating to their source, how they are transmitted, or their effects. The most important of these categories are discussed in
"College Physics: Normal, Tension, and Other Examples of Forces" 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/4-5-normal-tension-and-other-examples-of-forces. Access for free at https://openstax.org/books/college-physics/pages/1-introduction
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Section de manuel
Elasticity: Stress and Strain
We now move from consideration of forces that affect the motion of an object (such as friction and drag) to those that affect an object’s shape. If a bulldozer pushes a car into a wall, the car will not move but it will noticeably change shape. A change in shape due to the application of a force is
"College Physics: Elasticity: Stress and Strain" 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/5-3-elasticity-stress-and-strain. Access for free at https://openstax.org/books/college-physics/pages/1-introduction
Publiées par d'autres organisations sous licence libre, créditées comme elles le demandent. Les liens ouvrent leurs sites.
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