Energy Flashcards
Q: What is the principle of energy conservation as illustrated by the “blocks in the room” analogy?
A: The “blocks in the room” analogy illustrates energy conservation. The number of blocks (representing energy) always remains constant, though the blocks may be hidden in different places (like potential energy stored in various forms). Energy is conserved but may be difficult to directly observe.
Q: How can energy be measured if it is not directly visible, according to the “blocks in the room” analogy?
A: Even if energy (like the blocks) is hidden in different forms, we can measure it indirectly. For example, if blocks are hidden in a toy box, their number can be calculated by weighing the box. Similarly, energy can be inferred from its effects, such as changes in height or displacement.
Q1: What is the Law of Conservation of Energy?
A1: The Law of Conservation of Energy states that the total energy in an isolated system remains constant, even though it may change forms. Energy cannot be created or destroyed but only transferred or transformed between kinetic, potential, thermal, or other energy forms.
Q2: How do we measure energy if we can never “see” it directly?
A2: Energy can only be detected through its effects, such as heat, motion, or radiation. While we cannot observe energy itself, we have equations to calculate how much energy is present in various forms like kinetic or potential energy.
Q3: What are the two main classes of energy, and how are they different?
A3: The two main classes of energy are kinetic energy (energy associated with motion) and potential energy (energy stored due to position or interaction). Kinetic energy involves moving objects, while potential energy involves forces like gravity, elasticity, or chemical bonds.
Q4: What happens to potential energy as an object falls towards the Earth?
A4: As an object falls toward the Earth, its gravitational potential energy decreases while its kinetic energy increases. The total energy remains constant, but it shifts from potential to kinetic energy as the object gains speed.
Q5: How does the conservation of momentum differ from the conservation of energy?
A5: Conservation of momentum refers to the total momentum of an isolated system remaining constant before and after a collision. Unlike energy, which is a scalar quantity, momentum is a vector, so direction matters. The total momentum of the system in all directions must be conserved.
Q6: What are the two types of collisions and how do they differ?
A6: The two types of collisions are elastic and inelastic:
Elastic collisions: Both momentum and kinetic energy are conserved. No energy is lost to other forms like heat or deformation.
Inelastic collisions: Momentum is conserved, but kinetic energy is not. Some energy is transformed into other forms, such as sound, heat, or deformation.
Q7: How does Newton’s third law relate to the conservation of momentum?
A7: Newton’s third law states that for every action, there is an equal and opposite reaction. In a collision, the forces two objects exert on each other are equal and opposite, leading to a change in their velocities. This interaction ensures that the total momentum before and after the collision remains conserved.
Q8: What is an example of an inelastic collision, and how is energy transformed in it?
A8: A car crash is an example of an inelastic collision. The cars crumple and come to a stop, conserving momentum but losing kinetic energy, which is transformed into heat, sound, and deformation of the cars.
Q9: What factors influence the energy stored in an elastic potential energy system, such as a stretched rubber band?
A9: The energy stored in an elastic system depends on how much the material is stretched or compressed. The more you stretch the rubber band, the more potential energy is stored in the elastic material, which is released when the band snaps back.
Q10: How do physicists categorize energy and momentum in real-world collisions, such as in billiards?
A10: In real-world collisions like billiards, physicists observe how momentum and energy transfer between the balls. Momentum is conserved as the balls scatter in different directions, while energy can be conserved or partially lost depending on whether the collision is elastic or inelastic.
Why is momentum always conserved in collisions?
Answer: Momentum is always conserved in collisions due to the law of conservation of momentum, which states that in a closed system with no external forces, the total momentum before and after the collision remains constant.
What happens in a perfectly inelastic collision?
Answer: In a perfectly inelastic collision, the two colliding objects stick together after impact, resulting in the maximum possible loss of kinetic energy. Momentum is still conserved, but kinetic energy is not.
How do you calculate the final velocity of two objects after an inelastic collision?
Answer: The final velocity after an inelastic collision is calculated by conserving momentum:
vfinal = m1v1+m2v2/m1+m2
where m1 and m2 are the masses of the objects, and v1 and v2 are their initial velocities
