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Marble Leap

Newton's First Law of Motion states that an object will remain at rest or in uniform motion in a straight line unless acted upon by an external force.

To make an object travel in a circular path a centripetal force is required, in this acitiviy that force is removed, so the marble continues on a straight path.

Inertia causes this straight path to continue when we remove the centripetal force.

Inertia is the resistance of any physical object to any change in its velocity. This includes changes to the object's speed, or direction of motion. An aspect of this property is the tendency of objects to keep moving in a straight line at a constant speed, when no forces act upon them.


  • Describe a scenario that demonstrates the property of inertia.


  • Per Group:
    paper plate or aluminium pie pan with section cut out

Key Questions

  • What direction does the marble travel in when it reaches the gap? Why?

What To Do

Challenges students to roll a marble along the side of the pie pan in such a fashion that it leaps over the gap and continues it’s circular path.


  • Draw a free body diagram for circular motion.
  • What changes when the size of the gap in the pie plate is larger or much smaller?
  • When you a travelling in car and it takes a corner at speed, what does it feel like? Why?

Other Resources

Science World |Youtube | Inertia