Energy and work
52 flashcards covering Energy and work for the ACT Science section.
Energy and work are fundamental concepts in physics that describe how forces interact with objects to produce motion or change. Work occurs when a force causes an object to move in the direction of that force, like pushing a box across the floor. Energy, on the other hand, is the capacity to do work, existing in forms such as kinetic energy (motion) and potential energy (stored due to position or shape). Together, they help explain everyday phenomena, from a rolling ball to a swinging pendulum, and are key to understanding how energy is transferred and conserved in systems.
On the ACT Science section, energy and work often appear in questions involving data analysis, graphs of motion or energy transformations, and basic calculations from passages. You'll encounter multiple-choice items that test your ability to interpret energy conservation in scenarios, calculate work using formulas like force times distance, or analyze how variables affect energy states. Common traps include confusing kinetic and potential energy or overlooking units in problems, so focus on reading graphs carefully and applying concepts logically rather than memorizing equations.
Practice identifying energy types in real-world contexts to build intuition.
Terms (52)
- 01
Work
Work is the product of the force applied to an object and the displacement of the object in the direction of the force, measured in joules.
- 02
Energy
Energy is the capacity to do work or cause change, existing in various forms such as kinetic, potential, and thermal.
- 03
Kinetic Energy
Kinetic energy is the energy an object has due to its motion, calculated using the formula KE = 1/2 mv², where m is mass and v is velocity.
- 04
Gravitational Potential Energy
Gravitational potential energy is the energy an object has due to its position in a gravitational field, calculated as PE = mgh, where m is mass, g is gravity, and h is height.
- 05
Elastic Potential Energy
Elastic potential energy is the energy stored in an object when it is compressed or stretched, such as in a spring, calculated as PE = 1/2 kx², where k is the spring constant and x is the displacement.
- 06
Mechanical Energy
Mechanical energy is the sum of an object's kinetic and potential energy, which is conserved in the absence of non-conservative forces like friction.
- 07
Conservation of Energy
The law of conservation of energy states that energy cannot be created or destroyed, only transferred or transformed from one form to another in a closed system.
- 08
Work-Energy Theorem
The work-energy theorem states that the net work done on an object equals its change in kinetic energy, useful for solving problems involving forces and motion.
- 09
Power
Power is the rate at which work is done or energy is transferred, calculated as power equals work divided by time, and measured in watts.
- 10
Joule
A joule is the unit of energy or work in the SI system, equivalent to the work done by a force of one newton acting over a distance of one meter.
- 11
Watt
A watt is the unit of power, equal to one joule per second, representing the amount of energy used or work done per unit time.
- 12
Force in Work Calculation
In work calculations, force is the component of the applied force that acts in the direction of the object's displacement.
- 13
Displacement
Displacement is the straight-line distance an object moves from its initial to final position, which is used in the formula for work.
- 14
Angle in Work Formula
The angle in the work formula is the angle between the force vector and the direction of displacement, affecting the work as force times distance times the cosine of that angle.
- 15
Net Work
Net work is the total work done by all forces acting on an object, which equals the change in its kinetic energy according to the work-energy theorem.
- 16
Positive Work
Positive work occurs when the force and displacement are in the same direction, resulting in an increase in the object's kinetic energy.
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Negative Work
Negative work happens when the force and displacement are in opposite directions, such as friction opposing motion, leading to a decrease in kinetic energy.
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Zero Work
Zero work is done when the force is perpendicular to the displacement, like when an object moves horizontally while gravity acts downward.
- 19
Kinetic Energy Formula
The formula for kinetic energy is KE = 1/2 mv², where m is the mass of the object and v is its speed, used to quantify motion energy.
- 20
Potential Energy Formula
The formula for gravitational potential energy is PE = mgh, where m is mass, g is acceleration due to gravity, and h is the height above a reference point.
- 21
Work Formula
The formula for work is W = Fd cosθ, where F is the force, d is the displacement, and θ is the angle between force and displacement vectors.
- 22
Power Formula
The formula for power is P = W/t, where W is work done and t is time, or alternatively P = Fv for constant force and velocity.
- 23
Efficiency
Efficiency is the ratio of useful output energy or work to the total input energy, often expressed as a percentage, highlighting energy losses in real systems.
- 24
Energy Transformation
Energy transformation is the process by which energy changes from one form to another, such as kinetic to thermal energy due to friction.
- 25
Thermal Energy
Thermal energy is the internal energy of an object due to the kinetic energy of its molecules, often transferred as heat in energy processes.
- 26
Chemical Energy
Chemical energy is the potential energy stored in the bonds of chemical compounds, released during reactions like burning fuel.
- 27
Hooke's Law
Hooke's Law states that the force exerted by a spring is proportional to its displacement from equilibrium, F = -kx, which relates to elastic potential energy.
- 28
Conservative Forces
Conservative forces, like gravity, depend only on the initial and final positions, not the path taken, allowing for conservation of mechanical energy.
- 29
Non-Conservative Forces
Non-conservative forces, such as friction, depend on the path taken and dissipate energy, often converting it to thermal energy.
- 30
Friction and Work
Friction does negative work on a moving object, reducing its kinetic energy by converting it into thermal energy through heat.
- 31
Energy Diagrams
Energy diagrams are graphical representations showing the potential and kinetic energy of an object at different points, helping visualize conservation principles.
- 32
Calculating Work from Graphs
Work can be calculated from a force-distance graph by finding the area under the curve, which represents the energy transferred.
- 33
Common Mistake: Work and Force
A common mistake is confusing work with force; work requires both force and displacement, whereas force alone does not imply work is done.
- 34
Work Done by Gravity
Work done by gravity is the gravitational force times the vertical displacement, positive when an object falls and negative when it rises.
- 35
Spring Potential Energy Example
For a spring, elastic potential energy is calculated using PE = 1/2 kx², where x is the stretch or compression from equilibrium.
A spring with k = 100 N/m stretched 0.2 m has PE = 0.5 100 (0.2)^2 = 2 joules.
- 36
Kinetic Energy in Collisions
In collisions, kinetic energy is conserved in elastic collisions but not in inelastic ones, affecting the final speeds of objects.
- 37
Power in Daily Activities
Power calculation in daily activities involves dividing the work done, like lifting an object, by the time taken to do it.
- 38
Gravitational Force in Energy
Gravitational force provides the potential energy in systems, decreasing as objects fall and converting to kinetic energy.
- 39
Simple Machines and Work
Simple machines like levers and pulleys do not change the amount of work done but can change the force or distance required.
- 40
Energy Loss to Heat
In real systems, some energy is lost to heat due to friction, reducing the overall mechanical energy available.
- 41
Roller Coaster Energy
In a roller coaster, potential energy at the top converts to kinetic energy on the descent, illustrating conservation of energy.
- 42
Work Against Friction
Work done against friction is the force of friction times the distance, which must be overcome to maintain motion.
- 43
Instantaneous Power
Instantaneous power is the power at a specific moment, calculated as force times velocity at that instant.
- 44
Total Mechanical Energy
Total mechanical energy is the sum of kinetic and potential energy, remaining constant in ideal systems with no energy loss.
- 45
Escape Velocity
Escape velocity is the minimum speed needed for an object to escape a planet's gravitational pull, related to gravitational potential energy.
- 46
Pendulum Energy
In a pendulum, energy oscillates between kinetic at the bottom and potential at the highest points, demonstrating conservation.
- 47
Work by Multiple Forces
When multiple forces act, total work is the sum of work done by each force, affecting the net change in kinetic energy.
- 48
Energy in Circuits
In electrical contexts, energy is transferred as electrical potential energy, though ACT focuses more on mechanical forms.
- 49
Free Fall Energy
In free fall, gravitational potential energy fully converts to kinetic energy, with speed increasing as height decreases.
- 50
Efficiency Formula
Efficiency is calculated as (useful energy output / total energy input) × 100%, showing how effectively energy is used.
- 51
Kinetic Energy Units
Kinetic energy is measured in joules, which are equivalent to kg·m²/s², ensuring consistent units in calculations.
- 52
Potential Energy Reference Point
Potential energy is measured relative to a reference point, like ground level, where it is defined as zero for convenience.