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📘 Forces: Physics Foundations

Foundations of forces, Newton's laws, and equilibrium at college level

12
lessons
~30 min
to learn
Adults
level
Start the course →

What you’ll learn

  1. Defining Force as a Vector QuantityIdentify force as a vector with magnitude and direction and distinguish contact from field forces.Force is introduced through its vector properties and SI units. Learners separate contact forces from field forces using everyday examples. The chapter sets up consistent notation used throughout the course.
  2. Newton's First Law and InertiaState Newton's first law and apply it to identify net force and inertial reference frames.The first law is examined through quantitative examples of zero net force. Students calculate when an object remains at rest or moves uniformly. Inertial frames are contrasted with accelerating ones.
  3. Newton's Second Law and F = maApply Newton's second law to solve for unknown mass, acceleration, or net force in one dimension.The second law receives its algebraic form and unit consistency checks. Students rearrange the equation for different unknowns. Real mechanisms such as Atwood machines illustrate proportional relationships.
  4. Newton's Third Law and Action-Reaction PairsIdentify action-reaction pairs and distinguish them from balanced forces on a single object.Third-law pairs are located in diagrams of colliding or pushing objects. Students practice labeling which object experiences each force. Common misconceptions about internal forces are corrected with examples.
  5. Gravitational Force Near EarthCalculate weight from mass and distinguish true weight from apparent weight in accelerating frames.Gravitational force is derived from g = 9.80 m/s² and applied to free-fall problems. Apparent weight in elevators receives separate treatment. Data from NIST gravity tables anchor the numbers.
  6. Normal Force and Surface InteractionsDetermine normal force magnitude on horizontal and inclined surfaces.Normal force is shown to adjust to whatever value prevents penetration. Inclined-plane resolutions separate components systematically. Students solve problems where normal force differs from weight.
  7. Friction: Static and KineticApply the friction equations to find maximum static friction and kinetic friction values.Static and kinetic regimes are contrasted with coefficient tables. Problems include impending motion and constant-velocity sliding. Energy dissipation through friction is introduced qualitatively.
  8. Tension in Strings and CablesCalculate tension in systems with pulleys and accelerating masses.Tension is treated as an internal force that pulls equally at both ends of a light string. Atwood-machine solutions illustrate simultaneous equations. Real pulley friction is noted as a later correction.
  9. Hooke's Law and Spring ForcesUse Hooke's law to relate spring force, displacement, and stiffness constant.The linear spring equation is derived and applied to both extension and compression. Energy stored in the spring is linked to work done by the force. Oscillatory motion is previewed without full differential equations.
  10. Constructing Free-Body DiagramsDraw complete free-body diagrams for extended objects in two dimensions.Systematic labeling of every external force is practiced on blocks, pendulums, and vehicles. Students check that every arrow represents a real interaction. Diagrams are cross-verified against Newton's laws.
  11. Static Equilibrium ConditionsSolve two-dimensional equilibrium problems using ΣF = 0 and Στ = 0.Force and torque balance equations are written for rigid bodies. Worked examples include bridges and hanging signs. Students verify solutions by substituting numerical values back into the equations.
  12. Forces in Non-Uniform MotionApply Newton's laws to objects moving along curved paths or in accelerating frames.Centripetal force is expressed as the net radial component rather than a new force type. Banked-curve equations are derived and solved. Accelerating reference frames introduce fictitious forces briefly for context.

Questions this course answers

A satellite in orbit experiences which type of force from Earth?

Gravity is a field force that acts without physical contact, allowing satellites to remain under Earth's influence even in vacuum.

Match each force example to its category

Tension and friction require direct surface or object contact; gravity and magnetism act through fields across distances.

A book rests on a level table inside an airplane flying at constant 900 km/h. Which statement correctly applies Newton's first law?

Inside the plane moving at constant velocity, the frame is inertial. With no net horizontal force the book stays at rest relative to the plane, exactly as the first law requires.

In your own words, explain how an observer inside an accelerating elevator can tell the frame is non-inertial using Newton's first law.

In an inertial frame an object with zero net force moves uniformly. Inside an accelerating elevator a hanging mass swings or a dropped ball appears to accelerate sideways relative to the observer without any identifiable external force, proving the frame itself is accelerating and therefore non-inertial.

A 3 kg object receives a net force of 12 N to the right. What is its acceleration?

Dividing the 12 N net force by the 3 kg mass yields 4 m/s² in the same direction as the force.

A constant 10 N net force acts on an unknown mass. If acceleration is measured at 2 m/s², roughly how large is the mass?

Mass equals net force divided by acceleration, so 10 N / 2 m/s² = 5 kg.

Grounded in trusted sources

  • OpenStax
  • National Institute of Standards and Technology
  • NASA
  • OpenStax University Physics, Forces and Newton's Laws, https://openstax.org/books/university-physics-volume-1/pages/5-introduction
  • PhET, Forces and Motion: Basics, https://phet.colorado.edu/en/simulations/forces-and-motion-basics
  • Khan Academy, Forces and Newton's laws, https://www.khanacademy.org/science/physics/forces-newtons-laws
  • MIT OCW, 8.01 Classical Mechanics, https://ocw.mit.edu/courses/8-01sc-classical-mechanics-fall-2016/

Every Wunder lesson is built from real, reputable sources — never invented.

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