Bring Science Home A spinning science activity
Key concepts Physics Mass Gravity Kinetic energy Potential energy Introduction Background For a rolling object, kinetic energy is split into two types: translational (motion in a straight line) and rotational (spinning). So when you roll a ball down a ramp, it has the most potential energy when it is at the top, and this potential energy is converted to both translational and rotational kinetic energy as it rolls down. This leads to the question: Will all rolling objects accelerate down the ramp at the same rate, regardless of their mass or diameter? The answer depends on the objects’ moment of inertia, or a measure of how “spread out” its mass is. If two cylinders have the same mass but different diameters, the one with a bigger diameter will have a bigger moment of inertia, because its mass is more spread out. Similarly, if two cylinders have the same mass and diameter, but one is hollow (so all its mass is concentrated around the outer edge), the hollow one will have a bigger moment of inertia. Does moment of inertia affect how fast an object will roll down a ramp? Give this activity a whirl to discover the surprising result! Materials
But it is incorrect to say “the object with a lower moment of inertia will always roll down the ramp faster.” It takes a bit of algebra to prove (see the "Hyperphysics" link below), but it turns out that the absolute mass and diameter of the cylinder do not matter when calculating how fast it will move down the ramp—only whether it is hollow or solid. So, in this activity you will find that a full can of beans rolls down the ramp faster than an empty can—even though it has a higher moment of inertia. (It has the same diameter, but is much heavier than an empty aluminum can.) Applying the same concept shows two cans of different diameters should roll down the ramp at the same speed, as long as they are both either empty or full. The same principles apply to spheres as well—a solid sphere, such as a marble, should roll faster than a hollow sphere, such as an air-filled ball, regardless of their respective diameters. More to explore This activity brought to you in partnership with Science Buddies Discover world-changing science. Explore our digital archive back to 1845, including articles by more than 150 Nobel Prize winners. Subscribe Now!
An inflated balloon has potential energy in the stretched rubber.
Potential energy is the energy stored within an object, due to the object's position, arrangement or state. Potential energy is one of the two main forms of energy, along with kinetic energy.
Kinetic energy used to compress a spring is stored as potential energy until released.
Potential energy is energy that is stored – or conserved - in an object or substance. This stored energy is based on the position, arrangement or state of the object or substance. You can think of it as energy that has the 'potential' to do work. When the position, arrangement or state of the object changes, the stored energy will be released. For example, it requires energy to compress a spring – but what happens to that energy once the spring has been compressed? After all, we know that energy cannot be created or destroyed, it can only be converted from one form to another. Well, in the case of our spring, the kinetic energy used to compress the spring has been converted to potential energy. When we release the spring, the stored potential energy will be converted back into kinetic energy.
There are two main types of potential energy:
Higher objects (with further to fall) have greater potential energy. The heaviest of 2 objects at the same height has the greatest gravitational potential energy.
Gravitational potential energy is energy in an object that is held in a vertical position, due to the force of gravity working to pull it down. The amount of gravitational potential energy an object has depends on its height and mass. The heavier the object and the higher it is above the ground, the more gravitational potential energy it holds. Gravitational potential energy increases as weight and height increases. Potential energy is energy that is stored in an object or substance. Gravitational potential energy is energy in an object that is held in a vertical position. Elastic potential energy is energy stored in objects that can be stretched or compressed. Elastic potential energyElastic potential energy is energy stored in objects that can be stretched or compressed, such as trampolines, rubber bands and bungee cords. The more an object can stretch, the more elastic potential energy it has.
Examples of potential energy include:
A rock sitting on the edge of a cliff. If the rock falls, the potential energy will be converted to kinetic energy, as the rock will be moving.
A stretched elastic string in a longbow. When the elastic string is released, it will cause the arrow to shoot forward.
A sparkler. The chemical potential energy in a sparkler will be released when the top of the stick is lit.
The food we eat. Food contains chemical potential energy – as our bodies digest it, the stored energy is converted into energy for us to move and grow.
A swimmer's gravitational potential energy is converted to kinetic energy on diving.
Potential energy is energy that is stored in an object or substance. Gravitational potential energy is energy in an object that is held in a vertical position. Elastic potential energy is energy stored in objects that can be stretched or compressed.
The term 'potential energy' was first used by a Scottish engineer called William Rankine during the 19th century.
The concept of potential energy dates all the way back to the ancient Greek philosopher, Aristotle.
A spring stores elastic potential energy because it can be stretched or compressed.
Potential energy is energy that is stored in an object or substance. The two main types of potential energy are gravitational potential energy and elastic potential energy. |