Physics kinematics
58 flashcards covering Physics kinematics for the MCAT Chem / Phys / Psych / Soc section.
Kinematics is a fundamental part of physics that deals with the motion of objects, without considering the forces that cause that motion. It focuses on describing how things move through space, using concepts like displacement, velocity, acceleration, and time. For example, you might calculate how far a car travels while speeding up or analyze the path of a thrown ball. This topic provides the building blocks for understanding more complex physical phenomena, making it essential for grasping real-world applications in science and medicine.
On the MCAT, kinematics appears in the Chemical and Physical Foundations section, often as multiple-choice questions involving problem-solving with equations or interpreting motion graphs. Common traps include confusing average speed with instantaneous velocity or overlooking vector directions, which can lead to incorrect answers. Focus on mastering the four key kinematic equations, practicing with scenarios like projectile motion or free fall, and visualizing problems with sketches to avoid errors.
Remember to always label your variables clearly when solving problems.
Terms (58)
- 01
Displacement
Displacement is the straight-line distance from the initial to the final position of an object, including direction, and is a vector quantity measured in meters.
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Distance
Distance is the total path length traveled by an object, regardless of direction, and is a scalar quantity typically measured in meters.
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Speed
Speed is the rate of change of distance with respect to time, a scalar quantity measured in meters per second, and does not indicate direction.
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Velocity
Velocity is the rate of change of displacement with respect to time, a vector quantity measured in meters per second, and includes both magnitude and direction.
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Acceleration
Acceleration is the rate of change of velocity with respect to time, a vector quantity measured in meters per second squared, and can indicate speeding up, slowing down, or changing direction.
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Average velocity
Average velocity is the total displacement divided by the total time taken, a vector quantity that gives the net direction and rate of displacement over an interval.
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Instantaneous velocity
Instantaneous velocity is the velocity of an object at a specific moment in time, determined by the slope of the position-time graph at that point.
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Average acceleration
Average acceleration is the change in velocity divided by the time interval over which the change occurs, a vector quantity useful for analyzing motion over periods.
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Instantaneous acceleration
Instantaneous acceleration is the acceleration of an object at a precise instant, found by the slope of the velocity-time graph at that moment.
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Kinematic equations
Kinematic equations are a set of four formulas relating displacement, initial velocity, final velocity, acceleration, and time for objects under constant acceleration.
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First kinematic equation
The first kinematic equation, v = u + at, relates final velocity to initial velocity, acceleration, and time, assuming constant acceleration.
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Second kinematic equation
The second kinematic equation, s = ut + (1/2)at^2, calculates displacement based on initial velocity, time, and constant acceleration.
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Third kinematic equation
The third kinematic equation, v^2 = u^2 + 2as, connects final velocity, initial velocity, acceleration, and displacement without directly using time.
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Fourth kinematic equation
The fourth kinematic equation, s = (u + v)t / 2, determines displacement using average velocity and time for constant acceleration.
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Position-time graph
A position-time graph plots an object's position against time, where the slope at any point represents the instantaneous velocity.
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Velocity-time graph
A velocity-time graph plots velocity against time, where the slope indicates acceleration and the area under the curve gives displacement.
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Acceleration-time graph
An acceleration-time graph plots acceleration against time, where the area under the curve represents the change in velocity.
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Slope of position-time graph
The slope of a position-time graph at any point equals the instantaneous velocity, helping to analyze how speed changes over time.
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Area under velocity-time graph
The area under a velocity-time graph represents the displacement of the object, allowing calculation of total distance traveled in a given direction.
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Free fall
Free fall is motion under gravity alone, where acceleration is constant at approximately 9.8 m/s^2 downward, ignoring air resistance.
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Projectile motion
Projectile motion is the curved path of an object launched into the air, combining horizontal uniform motion and vertical accelerated motion due to gravity.
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Horizontal velocity in projectile
In projectile motion, horizontal velocity remains constant because no horizontal acceleration acts, assuming no air resistance.
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Vertical velocity in projectile
In projectile motion, vertical velocity changes due to gravity, starting from an initial value and reaching zero at the highest point.
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Time of flight for projectile
Time of flight is the total time a projectile is in the air, calculated using vertical motion equations and depending on initial height and launch angle.
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Maximum height of projectile
Maximum height is the highest point reached by a projectile, found by setting vertical velocity to zero in the kinematic equations.
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Range of projectile
Range is the horizontal distance traveled by a projectile, maximized at a 45-degree launch angle on level ground, calculated using motion equations.
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Relative velocity
Relative velocity is the velocity of one object as observed from another moving object, found by vector subtraction of their velocities.
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Uniform motion
Uniform motion occurs when an object travels at a constant velocity, meaning equal displacements over equal time intervals.
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Uniformly accelerated motion
Uniformly accelerated motion is when an object's acceleration is constant, allowing use of kinematic equations to predict position and velocity.
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Initial velocity
Initial velocity is the velocity of an object at the start of a motion interval, often denoted as u, and is crucial for solving kinematic problems.
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Final velocity
Final velocity is the velocity of an object at the end of a motion interval, denoted as v, and can be calculated using acceleration and time.
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One-dimensional motion
One-dimensional motion occurs along a straight line, simplifying kinematics to scalar or vector analysis in a single direction.
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Two-dimensional motion
Two-dimensional motion involves movement in a plane, like projectile motion, requiring separate analysis of horizontal and vertical components.
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Parabolic path
A parabolic path is the trajectory of a projectile under constant acceleration, resulting from the combination of constant horizontal velocity and linear vertical acceleration.
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Independence of motion components
In projectile motion, the horizontal and vertical components are independent, meaning changes in one do not affect the other.
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Vector quantity
A vector quantity has both magnitude and direction, such as velocity or acceleration, and must be treated with vector operations in kinematics.
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Scalar quantity
A scalar quantity has only magnitude, like speed or distance, and is added algebraically without considering direction.
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Deceleration
Deceleration is negative acceleration, slowing an object down, and is analyzed using the same kinematic equations as acceleration.
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Strategy for kinematic problems
A strategy for kinematic problems involves identifying known variables, selecting the appropriate equation, and solving for the unknown while checking units.
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Common trap: Average vs. instantaneous
A common trap is confusing average velocity, which is total displacement over time, with instantaneous velocity, which is speed at a specific moment.
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Units in kinematics
Units in kinematics, such as meters for displacement and seconds for time, must be consistent, typically in SI, to ensure accurate calculations.
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Dimensional analysis
Dimensional analysis checks if kinematic equations are balanced by ensuring both sides have the same units, like meters per second for velocity.
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Example: Object at rest accelerating
For an object starting from rest with constant acceleration, displacement can be found using s = (1/2)at^2, illustrating basic kinematics.
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Example: Ball thrown upward
A ball thrown upward reaches maximum height when velocity is zero, then falls, demonstrating how acceleration due to gravity affects motion.
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Calculating time to stop
Time to stop is calculated using v = u + at when final velocity is zero, such as a car braking from initial speed.
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Velocity from position graph
Velocity can be derived from a position-time graph by finding the slope, which directly gives the rate of change at any point.
- 47
Displacement from velocity graph
Displacement is obtained by calculating the area under a velocity-time graph, providing a visual way to find net distance with direction.
- 48
Motion with constant velocity
Motion with constant velocity means no acceleration, so displacement equals velocity multiplied by time, resulting in a straight position-time graph.
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Effect of gravity on vertical motion
Gravity causes constant downward acceleration in vertical motion, altering velocity while horizontal motion remains unaffected.
- 50
Resolving vectors in kinematics
Resolving vectors involves breaking them into components, like x and y, to simplify analysis of two-dimensional motion.
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Free fall from rest
In free fall from rest, velocity increases linearly with time at g = 9.8 m/s^2, and distance fallen is s = (1/2)gt^2.
- 52
Projectile launch at angle
For a projectile launched at an angle, initial velocity is resolved into components to calculate trajectory and landing point.
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Relative motion in one dimension
Relative motion in one dimension is the difference in speeds if objects move along the same line, helping determine closing or overtaking.
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Kinematics in circular motion
In uniform circular motion, speed is constant but velocity changes due to direction, leading to centripetal acceleration.
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Average speed calculation
Average speed is total distance divided by total time, often differing from average velocity when direction changes.
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Trap: Ignoring initial conditions
A trap in kinematics is overlooking initial velocity or position, which can lead to incorrect predictions of final motion.
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Using graphs for prediction
Graphs in kinematics predict future positions or velocities by extending lines, such as extrapolating a velocity-time graph.
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Symmetry in projectile motion
Symmetry in projectile motion means the time to rise equals the time to fall for the same vertical distance, aiding in quick calculations.