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, learn why a force can never exist on its own, and see why physicists insist on drawing forces as arrows rather than writing them as plain numbers. 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.
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.
- Pairs of objects interact to produce a force on each other, which can be represented as vectors.
- Scalars are quantities that have magnitude only. Vectors are quantities that have direction as well as a magnitude. A vector quantity may be represented by an arrow. The length of the arrow represents the magnitude and the direction of the arrow represents the direction of the vector quantity. Students should be aware that distance, speed and time are examples of scalars and displacement, velocity, acceleration, force and momentum are examples of vectors.
- Weight is the force acting on an object due to gravity. The weight of an object depends on the gravitational filed 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.
Carte mentale
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Note de cours
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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 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.
- Which of these is a non-contact force? A. Friction B. Tension C. Magnetism D. Normal contact force Answer: C
- Which quantity is a vector? A. Distance B. Speed C. Mass D. Acceleration Answer: D
- 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
- A spring is 40 mm long with no load on it. A load stretches it to a length of 70 mm. What is the extension of the spring in metres? A. 0.030 m B. 0.040 m C. 0.070 m D. 0.110 m Answer: A
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