# Angular energy vs translational energy

• GnG.Vike13
In summary, the conversation discusses the rotational and translational kinetic energy of a rectangular block when it is tipped over and hits the ground. It is debated whether the block will have rotational, translational, or both types of kinetic energy when it lands, taking into consideration factors such as friction and the location of the weight vector. It is concluded that there will be a difference in the block's motion if there is no friction, and that the only way for there to be no translational energy is if a couple force is applied. The conversation also considers a scenario where the block is not tipping over and the frictional force is applied to the bottom side. In this case, it is suggested that the block will slide with only translational kinetic energy

#### GnG.Vike13

i don't understand this at all... if we tip over a rectangular block (such that a corner is its pivot), will it have rotational kinetical energy, translational kinetic energy, or both when it hits the ground?

Ask yourself "Is its centre of mass moving horizontally and or vertically with respect to the floor when it actually lands and is it rotating?"
How would things be different if there were no friction between the corner and the table (assuming you placed it just beyond its tipping angle?
What does that tell you about its translational and rotational KE, bearing in mind that the same amount of energy is available in each case.

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so the translational kinetic energy is based on its center of mass' velocity and the rotational energy is based on the I of the whole block and w?

and, just to be clear, the weight vector will always come from the center of mass, correct?

also, how would friction play into this? would it be at the axis of rotation, thus causing not torque, but preventing it from making a translational acceleration?

GnG.Vike13 said:
so the translational kinetic energy is based on its center of mass' velocity and the rotational energy is based on the I of the whole block and w?

and, just to be clear, the weight vector will always come from the center of mass, correct?

also, how would friction play into this? would it be at the axis of rotation, thus causing not torque, but preventing it from making a translational acceleration?

That seems the right idea. But there would be a definite difference if there were no friction. What would the block rotate around if the corner were allowed to slip? Would the cm ever be moving horizontally at all? Would the block take the same time to fall with and without friction?
Your statements about mvsquared/2 and Iωsquared/2 are obviously correct. I think the only way that there would be no translational energy would be if it were just a couple that was applied to the block so that the cm was not moving in any direction. This is definitely not the case here.

sophiecentaur said:
That seems the right idea. But there would be a definite difference if there were no friction. What would the block rotate around if the corner were allowed to slip? Would the cm ever be moving horizontally at all? Would the block take the same time to fall with and without friction?
Your statements about mvsquared/2 and Iωsquared/2 are obviously correct. I think the only way that there would be no translational energy would be if it were just a couple that was applied to the block so that the cm was not moving in any direction. This is definitely not the case here.

okay, it's good to know that i understand this. one more question, perhaps.

what happens if the block isn't tipping over and the frictional force is applied completely on block's bottom side? how do you look at the problem then?

Then, with sufficient force applied, won't it just slide with some translational KE and no rotational energy?

## What is the difference between angular energy and translational energy?

Angular energy is the energy associated with an object's rotation, while translational energy is the energy associated with an object's movement in a straight line.

## How are angular energy and translational energy related?

Angular energy and translational energy are both forms of kinetic energy, meaning they are both related to an object's motion. However, they involve different types of motion - rotation and linear movement.

## Which type of energy is conserved in a spinning object?

Angular energy is conserved in a spinning object, as long as no external torque is acting on the object. This means that the amount of angular energy remains constant, and can only be changed by an external force.

## How is angular energy measured?

Angular energy is typically measured in joules (J), the same unit used for measuring translational energy. However, for rotating objects, it can also be measured in radians per second (rad/s) or revolutions per minute (RPM).

## What are some real-world examples of angular energy and translational energy?

Some examples of angular energy include a spinning top, a rotating wind turbine, and a spinning figure skater. Examples of translational energy include a car moving down a road, a person running, and a thrown ball.