Balanced and unbalanced forces simulator

What this simulator shows

A force is a push or a pull, measured in newtons (N). This simulator shows a box with four force arrows: a push to the left, a push to the right, a force up and a force down. Plus and minus buttons set each one from 0 to 10 newtons, and the arrow length grows with the size of the force. The readout works out the resultant force, the overall force left–right and up–down, and says whether the forces are balanced or unbalanced.

• Balanced forces: the forces cancel out, so there is no change in motion. A still box stays still, and a moving box keeps moving at the same speed in the same direction.
• Unbalanced forces: there is a resultant force, so the motion changes. The box speeds up, slows down or changes direction, toward the bigger force.
• To find the resultant in one direction, subtract the smaller force from the bigger one. 7 N right and 3 N left give 4 N to the right.

Common misconceptions

The biggest misconception about forces is that a moving object needs a force to keep it moving, so balanced forces must mean the object is still. Balanced forces mean no change in motion. A car cruising at a steady speed on a straight road has balanced forces: the push from the engine matches the friction and air resistance. This is Newton's first law of motion, and it still surprises many adults.

Other mix-ups: thinking an object resting on a table has no forces on it (gravity pulls it down and the table pushes it up with an equal force), or that an unbalanced force always makes something speed up. A force against the direction of motion, such as brakes or friction, slows it down. The readout mentions both.

Where this fits in school

• US, grade 3: NGSS 3-PS2-1 asks students to investigate the effects of balanced and unbalanced forces on the motion of an object.
• US, grades 6 to 8: NGSS MS-PS2-2 asks students to show that a change in an object's motion depends on the sum of the forces on it and its mass.
• England, Year 5: pupils explore gravity, air resistance, water resistance and friction, and how forces act between moving surfaces.
• England, Key Stage 3: pupils use force arrows in diagrams, add forces in one dimension, and study balanced and unbalanced forces and how they change speed or direction.

A 10-minute forces activity

• Press Start again so every force is 0. Ask: "What will happen to a still box with no forces?" (nothing changes).
• Set left and right to 5 N each. Ask whether the box will move. Read the readout together.
• Raise the right push to 8 N. Ask the student to work out the resultant before reading it (3 N to the right).
• Set down to 6 N for the box's weight. Ask what force a table would need to give to hold it up (6 N up).
• Ask the student to describe a real situation that matches one of their set-ups, such as a tug of war.

A simple tug of war, or two people pushing a box from opposite sides, shows the same idea with real forces. Spring scales, if available, let students measure forces in newtons themselves.

Learning more

Science is part of Eurekami's skill map, with lessons that draw science diagrams live and narrate them in English or Spanish. When a forces question is tricky, the AI tutor asks guiding questions so the student does the reasoning.