Read the notes, then try the practice. It adapts as you go.When you're ready.
Session Length
~17 min
Adaptive Checks
15 questions
Transfer Probes
8
Newton's three laws of motion form the foundation of classical mechanics and explain how objects behave when forces act on them. The first law (law of inertia) states that an object remains at rest or moves at constant velocity unless a net external force acts upon it. The second law quantifies this relationship with the equation F = ma, linking net force, mass, and acceleration. The third law establishes that every action force has an equal and opposite reaction force acting on a different object.
Building correct intuitions about these laws requires confronting several persistent misconceptions. Many students believe that motion requires a continuous force, that heavier objects fall faster, or that action-reaction pairs cancel each other out. Working through carefully designed problems, especially free-body diagrams and multi-object systems, helps replace these naive ideas with accurate physical reasoning.
Newton's laws connect directly to nearly every other topic in mechanics, including friction, projectile motion, circular motion, and momentum conservation. Mastering these laws provides the analytical toolkit needed to solve problems ranging from elevator physics and Atwood machines to vehicle collisions and orbital mechanics.
One step at a time.
Adjust the controls and watch the concepts respond in real time.
An object at rest stays at rest, and an object in motion stays in motion at constant velocity, unless acted upon by a net external force.
Example: A hockey puck sliding on ice continues moving in a straight line until friction or a stick changes its motion.
The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass, expressed as F = ma.
Example: Pushing an empty shopping cart accelerates it more than pushing a full one with the same force, because the full cart has greater mass.
For every action force, there is an equal and opposite reaction force. These forces act on different objects simultaneously.
Example: When you push against a wall, the wall pushes back on your hands with an equal force in the opposite direction.
The vector sum of all forces acting on an object. When net force is zero, the object is in equilibrium and does not accelerate.
Example: A book resting on a table has gravity pulling it down and the normal force pushing it up; these cancel out so the net force is zero.
A simplified drawing that shows all the forces acting on a single object as arrows pointing in the direction each force is applied.
Example: Drawing a box on a ramp with arrows for gravity, normal force, and friction helps you determine the net force along and perpendicular to the surface.
Mass is the intrinsic quantity of matter in an object (measured in kg) and does not change with location. Weight is the gravitational force on that mass (W = mg) and varies with the local gravitational field strength.
Example: An astronaut has the same mass on the Moon as on Earth, but weighs about one-sixth as much because the Moon's gravitational acceleration is roughly 1.6 m/s^2 instead of 9.8 m/s^2.
A state in which the net force on an object is zero. Static equilibrium means the object is at rest; dynamic equilibrium means it moves at constant velocity.
Example: A book on a table is in static equilibrium (net force zero), while a car cruising at constant speed on a straight highway is in dynamic equilibrium.
The perpendicular contact force exerted by a surface on an object. It adjusts in magnitude to prevent objects from passing through surfaces and plays a key role in friction calculations.
Example: When you stand on the floor, the floor pushes up on you with a normal force equal to your weight. On an incline, the normal force equals mg cos(theta) rather than the full weight.
Choose a different way to engage with this topic — no grading, just richer thinking.
Explore your way — choose one:
See how the key ideas connect. Nodes color in as you practice.
Walk through a solved problem step-by-step. Try predicting each step before revealing it.
This is guided practice, not just a quiz. Hints and pacing adjust in real time.
Small steps add up.
What you get while practicing:
The best way to know if you understand something: explain it in your own words.
More ways to strengthen what you just learned.