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Estimate stopping distance and mean force

A shorter stopping distance requires more force. An average stopping force does not determine the peak impact force.

Horizontal stopping with dashed first-contact position, compressed end position, rightward initial velocity and leftward average contact force.mvFavgsFirst contactStopped
Side-view concept of horizontal stopping against an absorber. Dashed position marks first contact; the right end is the stopped position. s is post-contact stopping travel; Favg is the magnitude of distance-average contact force opposing motion.

What you will understand

  • Separate contact stopping distance and control delay
  • Relate energy to distance-average force
  • Distinguish mean force, peak force and ratings

Blue: defined conditions · Red: calculated quantities. Diagrams are schematic.

  • m, v: mass and speed at contact
  • s: stopping travel after contact
  • Favg: contact force averaged over travel

The examples below are illustrative. Each example button loads its fixed values, units and mode. Ordinary calculator links do not load an example.

Define mass and speed at stopping

Distinguish horizontal travel from falling and use speed at first contact. Rotating inertia or a drive that continues pushing can add energy/work outside this simple model.

  • Total moving mass, contact speed and absorber travel
  • Drop height, gravity direction and continuing drive force

Calculate mean force from energy

For horizontal stopping with negligible work from other forces, kinetic energy divided by stopping travel gives distance-average contact force. It need not equal the time average or peak.

E=mv²/2, Favg=E/s (limited horizontal-stop model)

Example: stop 10 kg at 1 m/s over 20 mm

Inputs

  • Horizontal stop, m=10 kg, v=1 m/s
  • Post-contact stopping travel s=20 mm

Results

  • Energy to absorb E=5 J
  • Distance-average contact force Favg=250 N
  • At s=10 mm: 500 N for the same energy

250 N is not peak force. An illustrative 0.040 s duration requires constant deceleration. Peak force cannot be established without stiffness, deformation, damping and force history.

Load the fixed values, units and mode for this illustration. Then edit them for your conditions.

The 100 mm drop-height input is loaded but unused in horizontal mode.

This comparison changes only stopping travel to 10 mm.

Include travel during response delay

Do not mix post-contact travel s with travel before a sensor, controller or brake responds. With constant speed during delay, delay travel is v×td.

  • Example: at 1 m/s, a 0.1 s delay alone adds 100 mm
  • Check response, braking build-up and measured stop travel

For constant deceleration a, stopping distance=v td + v²/(2a)

Check cycle energy as well as force

Compare energy per cycle, thermal duty, peak force, stroke and eccentric load with actual component specifications. This reference calculation does not certify machine safety stopping performance or protective distances.

For practical review

During a drop, gravity continues doing work while stopping, so contact force is not contact kinetic energy/s alone. Continuing drive, spring force, rotational energy, slopes and elastic impact need their own work/energy accounting.

Keep a review checklist

This checklist is a personal reminder, not a safety score or an automatic approval. It is not sent or saved.

Continue with another guide

Reference information and illustrative calculations. This content does not guarantee suitability or safety of a design. Confirm the actual materials, component specifications and operating conditions.