In physics, energy is the capacity for doing work. This definition relates closely to our everyday understanding of energy. For instance, it is common to hear someone say, “I don’t have the energy for this right now”. What they mean is that they don’t have the capacity for doing whatever it is that they’re talking about doing.
Another close relative of the term ‘energy’ in everyday life is the use of the term ‘force’.
Growing up your mother may have yelled at you once or twice, “Don’t use too much force on that door!” when slamming the fridge or closet. What she really means is that you shouldn’t push or pull the door too hard. In this case, the term force is used to mean a push or a pull. This is another definition that relates closely to our everyday understanding of force.
Although the two terms, ‘force’ and ‘energy’, are typically used interchangeably in everyday language, they are quite different in physics. One involves an interaction of two or more bodies (for example, your hand and a door) whilst the other one is a little more abstract – like a feeling which boosts your ability to work.
What is force?
When two or more bodies come close enough to one another, they may interact. The interaction manifests itself in many forms that we call collectively call “force”.
Additionally, these “interactions” may happen through contact (such as dragging a box along the floor) or non-contact (such as the attraction of iron fillings by a magnet). Most scientists are simply comfortable defining force simply as a pull or a push. The push or pull has the effect of changing the state of motion (or rest) of a body.
A lot of what we know about forces in classical physics stems from ideas put forward by British physicist and mathematician, Sir Isaac Newton back in the mid-1660s.
What is energy?
When two or more bodies come close enough to one another, they may interact. The interaction manifests itself in many forms that we call collectively call “force”.
Additionally, these “interactions” may happen through contact (such as dragging a box along the floor) or non-contact (such as the attraction of iron fillings by a magnet). Most scientists are simply comfortable defining force simply as a pull or a push. The push or pull has the effect of changing the state of motion (or rest) of a body.
A lot of what we know about forces in classical physics stems from ideas put forward by British physicist and mathematician, Sir Isaac Newton back in the mid-1660s.
Ownership
Energy is something a body has – like money. When you have money, you have the capacity to purchase items and services. Likewise, when a body has energy, it has the capacity for doing work.
On the other hand, a body can’t have force. A force, by definition, is a push or pull upon an object resulting from the object’s interaction with another object – like when two people are fighting each other.
You cannot possess a “push” in the same way as you possess money.
Transfer and depletion
Energy can be transferred from one body to another, just as money can be transferred from one person to another.
A popular example of energy transfer is when you are climbing up the stairs. In this way, you are expending the energy stored in your body by transferring it to potential energy as you go up the ladder. If you climb up for too long, you’ll deplete yourself of energy and will have to rest and eat before you proceed.
Forces on the other hand are not transferrable and cannot be depleted. The force of gravity has been acting on you since the day you were born, it’ll be acting on you till the day you die and it will continue acting on your corpse till you decompose to natural gas or whatever. It cannot be depleted. Likewise, the force of gravity isn’t transferrable to any other forces, say, magnetic, electrical, or frictional force.
Forces appear and disappear all the time. When you and your friend share a hug, you are exerting forces on each other. Once you let go of each other, these forces simply vanish. They don’t transform into ‘other forms of forces’.
Energy though is never lost – it simply jumps from one form to another. In physics, we call this property conservation. If inflation wasn’t a problem, the value of a given amount of money would remain the same, regardless of how much it is circulated. We could say, money is conserved.
The question of isolation
Forces come in pairs – like a ballroom dance. In classical mechanics, any force acting on a body can be traced back to another object in its environment as the cause. Every force has a Source Object and Target Object. The general rule is this: Body A exerts a force on Body B and vice versa. For example, I push a car. Ronald punched Kevin. The car is sliding against the floor. Here is a deeper understanding of Newton’s action-reaction law.
No force exists in isolation. Friction happens when there is relative motion between two bodies in contact, the magnetic force doesn’t come to play unless there is a paper clip or another magnet nearby, and the only reason the force of gravity is acting on you is because you are close enough to Earth. If you were to go to infinity (wherever that is!) you wouldn’t feel a single pull of gravity.
But energy can exist in isolation, it doesn’t need other bodies. A body can have energy simply due to its state. A ball hanging in mid-air has potential energy associated with it, even when it is not moving. The glowing Sun has heat and light energy associated with it, even if all planets in the solar system were to disappear. The capacity of a body to do work is independent of external bodies and the environment.
Direction
Forces are directional – which sort of makes sense because it would be pointless to push or pull something without direction right? Several things may happen when a force acts on an object: it may start moving, speed up, slow down, stop, deform, or some combination of the above. Either way, the direction of importance.
Energy, however, isn’t bounded by direction. You’d burn the same amount of calories whether you are running East or West.
And that wraps up the differences between energy and force.
