Forces
Resumen
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.
Objetivos
- 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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- 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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