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Physics Exam Review: Forces
This review sheet covers the key concepts, definitions, and problem-solving skills you should know for the upcoming Forces exam.
1. Newton’s Laws of Motion
Newton’s First Law (Law of Inertia)
An object at rest stays at rest, and an object in motion stays in motion unless acted on by a net external force. If the net force is zero , the object’s velocity does not change. Objects with more mass have more inertia.
Newton’s Second Law
The acceleration of an object depends on the net force acting on it and its mass.
Formula:
Acceleration is in the same direction as the net force.
Units:
Force: Newtons (N)
Mass: kilograms (kg) Acceleration: m/s²
Newton’s Third Law
For every action force, there is an equal and opposite reaction force. Action–reaction pairs: Act on different objects Are equal in magnitude Are opposite in direction
2. Free Body Diagrams (FBDs)
A free body diagram shows all the forces acting on a single object.
∑ F = ma
Practice here: https://www.physicsclassroom.com/class/newtlaws/Lesson-2/Drawing-Free-Body-Diagrams
Steps to Draw a Free Body Diagram:
Draw the object as a dot or simple box Draw arrows for each force acting on the object Label each force clearly Arrows point in the direction the force acts Add a compass to determine orientation
Important Notes:
Only include forces acting on the object (not forces it exerts on others) Do not include motion or velocity arrows—only forces
3. Common Types of Forces
Weight
Force due to gravity
Acts straight downward toward the center of the Earth
Formula:
Normal Support force exerted by a surface Acts perpendicular to the surface Not always equal to weight Changes if other vertical forces are present or if the surface is angled
Tension Force exerted by a rope, string, or cable Always pulls away from the object Acts along the direction of the rope
Friction
Force that resists motion between two surfaces in contact
F g = mg
Check units in all calculations Read each problem carefully to identify all forces
Good luck studying!
