Read and check force diagrams

One target, several forces

A force diagram represents forces acting on one chosen object, called the target. Every force arrow belongs to that target. Its source label names what exerts the force

1. 1Direction The arrowhead points in the direction of the push or pull on the target
2. 2Strength Force strength is measured in newtons (N). On one fixed scale, a 6 N arrow is twice as long as a 3 N arrow
3. 3A model, not a scene The arrows represent forces, not physical cables or distances. The source objects need not be drawn

Build the diagram from the interactions

A block rests on a platform. The platform pushes it up with 4 N and Earth pulls it down with 4 N. Neglect air effects

1. 1Choose the target Draw and name the block. Include forces acting on the block, not forces it exerts on other objects
2. 2Add the directions and sources Draw an upward arrow for the platform and a downward arrow for Earth. Name each source
3. 3Compare lengths on one scale Both forces are 4 N, so draw equal-length arrows on one scale
4. 4Check the scope These are the two forces in this stated model. The block is at rest, but neither individual force is zero

This is the diagram just constructed. Which interaction does the upward arrow represent?

The target is the block. The source key pairs the upward arrow with the platform

Two cables pull a cart in opposite directions. If both pulls have the same strength, what should happen to their force-arrow lengths on one scale?

The right cable stays at 3 N. Set the left cable to 2 N, then 3 N, then 6 N. Compare their arrows with the fixed 6 N reference. Only the horizontal cable pulls are drawn; gravity, support and motion are not shown

At a left pull of 3 N, what does the drawing show?

Compare these two cable-force arrows. What does the difference in length mean?

Both arrows use the same 6 N reference. Compare 6 N with 3 N

Keep motion and forces separate

An object can be travelling one way while a force acts the other way. For example, a ball travelling upward still has downward gravity after it leaves the hand

1. 1Separate symbols Here solid arrows represent forces. A dashed cue, when supplied, gives current motion. It is not another force
2. 2Name a physical source Moving and at rest describe motion, not objects exerting forces. Do not add them as force-source labels
3. 3Read what is included A diagram showing only horizontal forces leaves out vertical forces on purpose. Missing arrows do not prove those forces have stopped acting
4. 4Check against the situation For each stated interaction, check the target, source, arrow direction and relative length. Do not change an arrow merely to match current motion

The cart is currently moving right. Which statement correctly reads this drawing?

Use the solid arrows for forces and the separately labelled dashed cue for current motion

A diagram of a trolley on a floor is captioned “Only the horizontal handle pull is shown.” It has no downward arrow. What can you conclude?

The caption deliberately limits the drawing. Decide what the missing arrow does, and does not, tell you

An iron ball on a horizontal surface is pulled left by a thread with 2 N and right by a magnet with 4 N. Only these horizontal forces are included. The proposed diagram contains an error. Which repair makes it match the stated interactions?

Check four features

Choose one target. Match each force arrow to its source, direction and strength. Compare lengths only on the same force scale, and keep any motion cue separate

1. 1A diagram needs a stated scope Say whether the drawing includes all forces in the model or only a selected group
2. 2Draw your own Sketch a block resting on a platform, with a 4 N upward force from the platform and a 4 N downward force from Earth. Compare the target, labels, directions and equal lengths. The app does not mark your drawing