Common Forces, Free-Body Diagrams and Connected Bodies

Name: Common Forces, Free-Body Diagrams and Connected Bodies
Author: StemPy Lab

A good picture solves half of a mechanics problem. In this course we meet the forces that act in everyday life: weight, the push of a surface, the pull of a string and the force of a spring. We learn to draw a free-body diagram for each body, and we use it for equilibrium, for a person in a lift, and for blocks joined by a string over a pulley.

3 lessons, about 1 h 15 min3 simulations12 problems6 practice questionsPython in every lesson

Created by StemPy Lab

Course outline (3 lessons)

Lesson 1about 25 min
Common forces: weight, normal reaction, tension and the spring force
Weight $W = mg$ is the Earth's pull, always down. The normal reaction is a surface's push at right angles to it, as big as it needs to be. Tension is the pull of a string, the same all along a light string. A spring pushes or pulls with $F = kx$ (Hooke's law), in proportion to its stretch or squash.
1 simulation2 practice questions1 Python program4 problems1 Python lab1 question set
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Lesson 2about 25 min
Free-body diagrams, equilibrium and the lift
A free-body diagram shows one body alone with every force on it, and nothing else. Then the second law is applied along convenient axes. A body in equilibrium has zero net force, so the forces along each axis balance. In a lift, the scale's push is $R = m(g + a)$ : more than the weight when the lift accelerates upward, less when it accelerates downward, zero in free fall.
1 simulation2 practice questions1 Python program4 problems
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Lesson 3about 25 min
Connected bodies and pulleys
Bodies joined by a light string move with the same speed and acceleration. Treat the whole system to find the acceleration (net outside force over total mass), then one body alone to find the tension. For an Atwood machine, $a = \dfrac{(m_1 - m_2)g}{m_1 + m_2}$ and $T = \dfrac{2m_1m_2g}{m_1 + m_2}$ ; the tension lies between the two weights.
1 simulation2 practice questions1 Python program4 problems1 Python lab1 note
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Equilibrium, Lifts and Pulleys: Practice Paper

20 questions · 50 min

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Common Forces, Free-Body Diagrams and Connected Bodies

Course outline (3 lessons)

Common forces: weight, normal reaction, tension and the spring force

Free-body diagrams, equilibrium and the lift

Connected bodies and pulleys

Test Your Learning

Your teacher

Discussion (0)