Force and motion
60 flashcards covering Force and motion for the ACT Science section.
Force and motion are core concepts in physics that explain how objects move and interact. Force is a push or pull that can speed up, slow down, or change the direction of an object, while motion describes the object's movement, such as its speed or path. These ideas are essential for understanding everyday phenomena, like why a car stops when you brake or how gravity keeps us on the ground. Mastering them helps build a foundation for more complex scientific topics.
On the ACT Science section, force and motion appear in questions that test data interpretation, such as analyzing graphs of velocity versus time or evaluating experiments on friction and acceleration. Common traps include mistaking constant speed for acceleration or overlooking variables like mass in force calculations. Focus on applying Newton's laws, recognizing balanced versus unbalanced forces, and practicing with real-world scenarios to avoid errors.
Remember to always label and check units in your calculations.
Terms (60)
- 01
Force
Force is a push or pull on an object that can cause it to accelerate, decelerate, or change direction, measured in newtons.
- 02
Net Force
Net force is the vector sum of all forces acting on an object, determining whether the object accelerates or remains at rest.
- 03
Motion
Motion is the change in position of an object over time, often described using concepts like speed and acceleration.
- 04
Speed
Speed is the rate at which an object covers distance, calculated as distance divided by time, and is a scalar quantity.
- 05
Velocity
Velocity is the speed of an object in a specific direction, making it a vector quantity that includes both magnitude and direction.
- 06
Acceleration
Acceleration is the rate of change of velocity over time, occurring when an object's speed or direction changes.
- 07
Newton's First Law
Newton's First Law states that an object at rest stays at rest, and an object in motion stays in motion at constant velocity, unless acted upon by a net force.
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Inertia
Inertia is the tendency of an object to resist changes in its state of motion, depending on its mass as described in Newton's First Law.
- 09
Newton's Second Law
Newton's Second Law states that the net force on an object equals its mass times its acceleration, expressed as F=ma.
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F=ma
F=ma is the formula from Newton's Second Law that relates net force, mass, and acceleration, allowing calculation of one variable when the others are known.
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Newton's Third Law
Newton's Third Law states that for every action force, there is an equal and opposite reaction force, acting on different objects.
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Action-Reaction Pair
An action-reaction pair consists of two forces that are equal in magnitude and opposite in direction, as per Newton's Third Law.
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Gravity
Gravity is the force of attraction between two masses, such as Earth pulling objects toward its center.
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Weight
Weight is the force exerted on an object due to gravity, calculated as mass times gravitational acceleration.
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Mass
Mass is the amount of matter in an object, a constant property that measures its inertia and is not affected by gravity.
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Friction
Friction is a force that opposes motion between two surfaces in contact, reducing the speed of moving objects.
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Static Friction
Static friction is the force that prevents an object at rest from starting to move when a force is applied.
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Kinetic Friction
Kinetic friction is the force that acts against an object that is already moving, generally less than static friction.
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Normal Force
The normal force is the perpendicular force exerted by a surface on an object resting on it, balancing the component of weight pressing down.
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Balanced Forces
Balanced forces are forces acting on an object that cancel each other out, resulting in no change in motion.
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Unbalanced Forces
Unbalanced forces are forces acting on an object that do not cancel, causing the object to accelerate in the direction of the net force.
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Displacement
Displacement is the straight-line distance from the initial to the final position of an object, a vector quantity.
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Distance
Distance is the total path length traveled by an object, regardless of direction, and is a scalar quantity.
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Average Speed
Average speed is the total distance traveled divided by the total time taken, providing an overall rate of motion.
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Instantaneous Speed
Instantaneous speed is the speed of an object at a specific moment in time, measured using a tangent on a distance-time graph.
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Uniform Motion
Uniform motion occurs when an object travels at a constant speed in a straight line, with equal distances covered in equal time intervals.
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Accelerated Motion
Accelerated motion is when an object's velocity changes over time, either in speed, direction, or both.
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Free Fall
Free fall is the motion of an object falling under gravity alone, with constant acceleration due to gravity.
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Gravitational Acceleration
Gravitational acceleration is the constant rate at which objects accelerate toward Earth, approximately 9.8 m/s² near the surface.
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Projectile Motion
Projectile motion is the curved path followed by an object launched into the air, influenced by gravity and initial velocity.
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Vector Quantity
A vector quantity has both magnitude and direction, such as velocity or force, and is represented by arrows in diagrams.
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Scalar Quantity
A scalar quantity has only magnitude, without direction, such as speed or distance.
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Momentum
Momentum is the product of an object's mass and velocity, a vector quantity that indicates the quantity of motion.
- 34
Conservation of Momentum
Conservation of Momentum states that in a closed system, the total momentum before a collision equals the total momentum after.
- 35
Impulse
Impulse is the change in momentum of an object, equal to the force applied multiplied by the time interval.
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Work
Work is the energy transferred to or from an object by a force acting over a distance, calculated as force times displacement in the direction of the force.
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Kinetic Energy
Kinetic energy is the energy an object possesses due to its motion, given by one-half times mass times velocity squared.
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Potential Energy
Potential energy is the stored energy an object has due to its position or configuration, such as gravitational potential energy.
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Mechanical Energy
Mechanical energy is the sum of kinetic and potential energy in a system, conserved in the absence of non-conservative forces.
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Power
Power is the rate at which work is done or energy is transferred, calculated as work divided by time.
- 41
Centripetal Force
Centripetal force is the net force that causes an object to move in a circular path, directed toward the center of the circle.
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Circular Motion
Circular motion is the movement of an object along a circular path, requiring a centripetal force to maintain the curve.
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Terminal Velocity
Terminal velocity is the constant speed reached by a falling object when the force of air resistance equals the force of gravity.
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Air Resistance
Air resistance is the frictional force exerted by air on a moving object, opposing its motion and affecting its speed.
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Hooke's Law
Hooke's Law states that the force exerted by a spring is proportional to its displacement from equilibrium, up to its elastic limit.
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Elastic Potential Energy
Elastic potential energy is the energy stored in a stretched or compressed spring, calculated using Hooke's Law.
- 47
Inelastic Collision
An inelastic collision is one where kinetic energy is not conserved, though momentum is, often resulting in deformation.
- 48
Coefficient of Friction
The coefficient of friction is a value that indicates the ratio of frictional force to the normal force between two surfaces.
- 49
Common Trap: Mass vs. Weight
Mass is the amount of matter in an object and remains constant, while weight is the gravitational force on that mass and varies with location.
- 50
Strategy for Solving Force Problems
To solve force problems, first draw a free-body diagram, identify all forces, calculate net force, and apply Newton's Second Law.
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Example: Calculating Acceleration from Force
If a 5 kg object experiences a net force of 20 N, acceleration is calculated as force divided by mass, resulting in 4 m/s².
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Example: Two Objects Colliding
In a collision, if a 2 kg object moving at 3 m/s hits a stationary 1 kg object, conservation of momentum helps determine their final velocities.
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Vector Addition
Vector addition combines vectors by adding their components, used to find resultant forces or velocities in multiple directions.
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Resultant Force
Resultant force is the single force that has the same effect as all individual forces acting on an object, found through vector addition.
- 55
Equilibrium
Equilibrium occurs when all forces on an object balance out, resulting in zero net force and no acceleration.
- 56
Torque
Torque is the rotational equivalent of force, calculated as force times distance from the pivot, causing an object to rotate.
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Simple Machines
Simple machines are basic devices like levers and pulleys that multiply force or change its direction to make work easier.
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Lever
A lever is a simple machine that consists of a rigid bar pivoting on a fulcrum, allowing a small force to move a large load.
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Pulley
A pulley is a simple machine that uses a wheel and rope to change the direction of a force, often to lift objects more easily.
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Inclined Plane
An inclined plane is a simple machine that is a sloped surface, reducing the force needed to raise an object by increasing the distance.