Forces, weight and mass

Interactive lesson
A force is an interaction between two objectsInteractive lesson
The newtonInteractive lesson
Force is a vectorInteractive lesson
Spot the weight forceInteractive lesson
Spot the normal forceInteractive lesson
The normal force is perpendicular to the surfaceInteractive lesson
TensionInteractive lesson
Spot the tension forcesInteractive lesson
Friction acts along the surface, against slidingInteractive lesson
Spot the friction force and its directionInteractive lesson
Drag (air resistance)Interactive lesson
Inventory the forces on an objectInteractive lesson
MassInteractive lesson
Weight

Weight, mass and free-body diagrams

Interactive lesson
Weight changes with location, mass does notInteractive lesson
Weight or mass? Judge the claimInteractive lesson
Weight equals mass times gInteractive lesson
Calculate the weightInteractive lesson
Find the unknown in w = mgInteractive lesson
Why weight changes but mass doesn'tInteractive lesson
What a free-body diagram isInteractive lesson
Read a free-body diagramInteractive lesson
Draw the free-body diagram: object resting on a surfaceInteractive lesson
Draw the free-body diagram: object pushed or draggedInteractive lesson
Draw the free-body diagram: hanging objectInteractive lesson
Draw the free-body diagram: falling objectInteractive lesson
Evaluate a flawed free-body diagramInteractive lesson
Net force from a free-body diagram

Newton's three laws

Interactive lesson
InertiaInteractive lesson
Newton's first lawInteractive lesson
EquilibriumInteractive lesson
In equilibrium or not?Interactive lesson
Does motion need a force? Judge the claimInteractive lesson
Why steady motion needs no forward forceInteractive lesson
Inertia and vehicle safetyInteractive lesson
Predict the motion when the net force vanishesInteractive lesson
Terminal velocityInteractive lesson
Net force drives accelerationInteractive lesson
Mass resists accelerationInteractive lesson
Newton's second law as an equationInteractive lesson
Acceleration points along the net force

Newton's second and third laws

Interactive lesson
The newton defined by the second lawInteractive lesson
Solve for the accelerationInteractive lesson
Solve for the net forceInteractive lesson
Solve for the massInteractive lesson
Only forces ON the object countInteractive lesson
Read the net-force direction off the motionInteractive lesson
Acceleration from a force scenarioInteractive lesson
Find the supporting force in an accelerating elevatorInteractive lesson
Newton's third lawInteractive lesson
Name the partner forceInteractive lesson
Third-law pair or balanced pair?Interactive lesson
Why third-law pairs never cancelInteractive lesson
Equal forces, unequal responsesInteractive lesson
Draw the pair on separate diagrams

Friction

Interactive lesson
Static frictionInteractive lesson
Kinetic frictionInteractive lesson
Static or kinetic? Decide which friction actsInteractive lesson
Friction grows with the normal forceInteractive lesson
The coefficient of frictionInteractive lesson
The kinetic friction lawInteractive lesson
What kinetic friction does not depend onInteractive lesson
Static friction adjusts up to a maximumInteractive lesson
Starting is harder than keeping goingInteractive lesson
Calculate a friction forceInteractive lesson
Will it slide?Interactive lesson
Find the unknown in f = μN

Friction and forces in two dimensions

Interactive lesson
The normal force is not always mgInteractive lesson
Acceleration of a sliding object with frictionInteractive lesson
Resolve a force into componentsInteractive lesson
Combine perpendicular forcesInteractive lesson
Find the unknown force that balancesInteractive lesson
Force needed for constant velocity against frictionInteractive lesson
Draw the free-body diagram: object on an inclineInteractive lesson
Resolve the weight on an inclineInteractive lesson
Acceleration down a frictionless inclineInteractive lesson
Connected objects share an accelerationInteractive lesson
Draw the free-body diagrams of a connected pairInteractive lesson
Solve a connected-objects system