Same Direction = Add • Opposite Directions = Subtract • Measured in Newtons (N)
The Dinner Table Hook: "Think of a paycheck. 'Gross' is what you earned, but 'Net' is what is left after taxes pull against it. If two people pull a rope with 20 N each from opposite sides, net force is 0 N, balanced, so nobody moves."
Measured in Newtons (N)If the arrows are pointing in the SAME direction, you ADD. If the arrows are pointing in OPPOSITE directions, you SUBTRACT.
The engine pushes forward with 800 N. Wind resistance and road friction push backward with exactly 800 N. Because 800 N − 800 N = 0 N, forces are BALANCED!
"If an object is moving fast, must the net force be greater than zero?"
NO! An unbalanced force is only needed to change speed (speed up, slow down, or turn). If speed and direction stay constant, Net Force is ALWAYS 0 N!
Downward Gravity = 15 N. The sturdy table pushes back upward with an equal Normal Force of 15 N. Net Vertical Force = 0 N (stays completely still!).
State assessments test whether motion is changing or constant. Classify each scenario!
The engine pushes the car forward with 800 N, and wind/road friction pushes backward with 800 N. What is the net force?
5 state-standard questions testing addition, subtraction, zero net force, and motion changes.