Science UNIT 3 Study Guide PDF
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This document is a study guide for a science unit on motion. It contains definitions and explanations of key physics concepts such as position, displacement, time, scalars, vectors, velocity, acceleration, and their associated mathematical relationships. It's intended for secondary school students.
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Position and Displacement - osition (d with a hat) → a vector quantity that shows an object’s distance and direction P from a reference point Measuring Time, Scalars, and Vectors - ords used to describe motion are distance, speed, position, time...
Position and Displacement - osition (d with a hat) → a vector quantity that shows an object’s distance and direction P from a reference point Measuring Time, Scalars, and Vectors - ords used to describe motion are distance, speed, position, time, etc W - Quantities that are measured or counted have a MAGNITUDE but may also contain a DIRECTION - Scalars: quantities that describe magnitude, but do not include direction (time, distance, speed, mass) - Vector quantities: quantities that describe magnitude and also include direction (position, displacement, velocity, acceleration, force) - Distance (d): a scalar quantity that describes the length of a path between two points or locations - SI unit for position and distance is m or km - Reference point: the starting point you choose to describe the location, or position, of an object - Motion: the process of changing position - Time interval (delta t): scalar, it is the difference between the final and initial time (delta t = final time - initial time) - Objects in uniform motion travel equal displacements in equal time intervals - Objects in uniform motion do not speed up, slow down, or change direction - Position-time graph: plots position data on the vertical axis and time data on the horizontal axis - Best fit line: a smooth or straight line that most closely fits the general shape outlined by the points - Uniform motion is represented by a straight line on a position time graph - The straight line passes through all plotted points Types of slope: - Positive slope (slants up to the right, indicates motion in the direction of the positive y-axis (uniform motion) - Zero slope (horizontal line, indicates that the object is not moving (neither uniform nor non-uniform) - Negative slope (slants down to the right, indicates motion in the direction of the negative y-axis (uniform motion) Displacement, Time, and Velocity isplacement (delta d with a hat, si unit is m/km): describes the straight line distance and D direction from one point to another (delta d with a hat = final position - initial position; change in position) Speed (v): the distance an object travels during a given time interval divided by the time interval (SI, m/s), speed = distance/time - The steeper the slope, the greater the change in displacement during the same tiem interval - verage velocity (Big V, small avg, with hat on top) the rate of change in position for a A time interval - Positive slope = forward, negative slope = backward, zero slope = zero Acceleration (and Velocity-time graphs), multiple choices, calculate elocity: the displacement of an object during a time interval divided by the time interval (delta d with a V hat divided by delta t) Acceleration: the change in an object’s velocity in a given amount of time (SI unit: m/s squared) Constant Velocity: An object traveling with uniform motion in a straight line Change in Velocity: The change that occurs when the speed of an object changes, or its direction of motion changes, or both Increasing the stopping time= decreases the acceleration Decreasing the stopping time= increases the acceleration Theslopeof the velocity-time graph is theaverage acceleration m/s2 Positive slope=positive acceleration(object velocity is increasing in the forward direction) Zero slope=Zero acceleration(object velocity is constant) Negative slope=Negative acceleration(object velocity is decreasing in the forward direction or increasing/speeding up in the backward direction) Equation: a with a hat = v with a hat (change in velocity) / t with a hat (time interval) Aristotle, Galileo Galilei, and Sir Isaac Newton on Motion Ideas- multiple ristotle: was curious about how objects would move if there were no outside forces (like gravity) acting A on them - His theories: → Falling bodies fall at a constant speed. → Falling bodies fall faster if they are heavier, → Falling bodies fall slower if they are met by some sort of resistance, → Every object on Earth has a natural motion or attraction towards the center of Earth (now known as gravitational attraction) → must apply a force to move an object, keep applying to keep the object moving Galileo: a true “Renaissance thinker”, didn’t agree with Aristotle, disproved his theories, made a U-shaped inclined plane experiment, and wasn’t always correct - His theories: → Once you stop applying force to an object, friction will slow the object down to a complete stop. → A body in motion will continue in motion at the same speed unless a force acts on the object from the opposite direction. → In a vacuum, with all forces of friction removed, all objects fall at the same speed regardless of their mass. → An object falling freely through the air, or rolling freely down an inclined plane will undergo a constant acceleration. Newton: described acceleration as an imbalance in forces (if there is a force acting on your right side, but there is a stronger force acting on your left side, you will be moved to the right. His first law of motion is still used today, and the characteristic matter to resist changes in motion is called inertia (Newton’s first law of motion = Newton’s law of inertia) Newton's Laws- calculate, multiple choice, true/false orce: any influence that alters or causes motion. You exert a force whenever you push or pull an object F (a vector quantity), forces happening in the same direction will strengthen each other, but forces in opposite directions will cancel each other out The first law of motion: - “An object at rest will remain at rest unless acted upon by an unbalanced force. An object in motion will remain in motion in a straight line at a constant velocity unless acted on by an unbalanced force. - Inertia is the tendency of an object to resist change - Formula: Net (total) force = Force A + Force B - Fnet (with a hat) = F A (with a hat) + F B (with a hat) - Newton’s first law only applies to objects moving at a constant speed and when the object is at rest. - The forces acting on an object must be balanced for it to remain at rest (not in uniform motion). The second law of motion - “When a force acts on a mass, acceleration is produced. The greater the mass, the greater the amount of force needed to cause acceleration. - Formula = F (with a hat) = m x a(with a hat) - SI = F = N (newton), m (kg), and acceleration (m/s squared) - Force = the force acting on the object - Mass = how much matter in an object - In a vacuum, all objects fall at the same rate regardless of their mass. Third Law of Motion - For every action, there is an equal and opposite reaction. - Action force: The force that initiates the action - Reaction force: The force that responds to the initial reaction - Example 1: You push on a door to open it. (Action: You push on the door, Reaction: The door pushes on you) - Example 2: You throw a baseball to your friend. (Action: Your hand pushes the ball, towards your friend, Reaction: The ball pushes back on your hand.) -Momentum and Impulse ( Don’t worry about direction terminologies) Momentum- the amount of motion in an object → the greater the momentum of an object, the more difficult it will be to alter or change that object’s motion → to bring a moving object to a stop, its momentum must be reduced to 0 2 factors to determine momentum 1. Velocity: Fast-moving objects are difficult to stop 2. Mass: massive objects are also difficult to stop Formula for momentum: p (with a hat) = m x v (with a hat) SI: kg x m/s - The momentum of an object can change (velocity can change) - Two objects with the same mass might have different momentums, due to differences in velocity - All moving objects have momentum (objects have mass, their moving so they have velocity) - When an object speeds up, it gets momentum - Objects with different masses can have the same momentum when they have different velocities - Direction does matter with momentum, but we don’t consider using words - When objects collide, some momentum is lost - A tiny bullet can have more momentum than a big truck if it has a very high velocity Impulse: the force applied over an interval of time How can you reduce an object’s momentum to zero? 1) Apply a force 2) Increase the amount of time the force is applied (impulse) Formula: I (with a hat) = F (with a hat) x delta t (time interval) SI: NxS, or just NS - To stop the motion of a vehicle, its braking system applies force on wheels for a long period of time - But in collision, that same impulse is applied to a short amount of time, which can cause forces acting on the car, and damaging occupants - there are devices that use the impulse-momentum relationship to decrease the force applied on cars (air bags, seat belts) - Ex: tossing an egg on the concrete will crack the egg (large force applied for a split second), but we can bring its momentum to zero by throwing the egg into a cushion/mattress, extending the time interval, so the force is much less - First collision: in the example of a car colliding with a building, the impact involves the car and the building. The car’s momentum was reduced to zero, and the force was great but applied over a short period of time. Passengers will continue to move forward with the same momentum that the moving car had. - Second collisions: when the passengers of that car hit the steering wheel or other objects that will reduce their momentum to zero (safety devices are now used, such as air bags, seat belts, bumpers, head restaurants, crumple zones, child safety seats, and rollover protective structures) Conservation of Energy he law of conservation of energy → energy can not be lost or created, but can only be transformed, T converted into different forms of energy, and transferred between objects Ex: In a vehicle collision, energy is transferred from the car to the pavement, into specific areas of the car, and the driver & passengers (and can break them) Different types of energy: - Kinetic energy: the energy of motion - Potential energy: the energy of position with respect to the surface of the Earth (ex: an object falling from two stories up will not fall with as much force or acceleration as an object that falls from 16 floors up) - Heat energy: Energy of molecules in motion (ex: bending and breaking metals and plastics causes them to heat; heat in brakes and tires as they try to stop the vehicle) - Sound energy: the disturbance of molecules Energy can also be stored electrically, chemically, or in elastics and springs. kinetic energy reduced to zero → other forms of energy increases Ex: less motion → more sound and heat Total energy (stays the same) = kinetic energy + potential energy The Effects of Friction - or example, when you push off a skateboard, you will roll down the sidewalk quickly at F first, then slow, and eventually stop. - The first law of motion states that a moving object will continue to move until it encounters an opposing force, so a force is needed for the object to stop. - One of the opposing forces,frictionis theforce that opposes the motion, and it is whenevertwo surfaces slide against and grip one another - The amount of friction depends on… - What the surfaces are made of - The surface texture - Amount of force pressing the two surfaces together - Any substance that is between two surfaces (oil, glue for example) - You move longer on smooth surfaces but stop abruptly on surfaces like rough gravel or gooey mud - Friction depends on the surfaces that are in contact with - Dry pavement surfaces allow you to walk without slipping and sliding - Icy pavement surfaces reduce friction, so there is less force to oppose your motion - Adding sand to ice helps, because adding traction to the surface, so there is friction between your feet and the ground, and there is more controlled motion - Examples of conditions that can affect friction and motion include: - Road conditions(Icy, wet, snow-covered roads reduce friction, gravel and dirt roads increase friction, unless they are loose) - Weight of vehicle(Heavy vehicle has more friction in its tires than lighter vehicle) - Type of tire(snow tires have softer rubber, deeper treads, and even metal studs to increase friction, especially in winter, and racing tires are smooth) - Friction between two surfaces can be expressed as a decimal calledfrictional constant (k), the closer it is to zero, the greater the friction Different constants: - Dry Pavement: 0.06 - Wet Concrete: 0.10 - Snow and Ice: 0.15 Braking Distance - hen applying brakes in your car, there is friction created between the brake pads and W the rotating wheel, which makes your car slow down and stop - From the time you apply the brakes to the time you come to a complete stop, you are traveling a distance, and that distance you cover is calledbraking/stopping distance - Reaction time: the amount of time it takes for you to recognize a situation and react to it, this impacts braking distance (ex: it takes 2s for you to recognize there is a dog in front of your car and apply brakes, and that two seconds is your reaction time) Factors that can increase your reaction time (be careful!): - Alcohol: Being drunk will slow down your reaction time (it is a depressant) - Hallucinogenic drugs: slows down reaction time - Depressant drugs: slow down body activity, including reaction time - Driver fatigue: the more tired you are, the slower you will process information and react - Cold/allergy medications: can make you drowsy and affect reaction time Factors that can influence stopping distance that are out of your control: - oad conditions (slippery, wet, or snow-covered roads can reduce friction and R increase braking time). You must anticipate longer braking distance (slowing down and giving yourself plenty of room to stop) - Conditions of your brakes (worn-out brakes can increase stopping distance) - Tire condition (worn-out tires that don’t have enough tread to give traction can increase stopping distance) The Mathematical Relationship between Speed and Braking Distance - heir relationship: double your speed, the braking distance increases four times. T - Their equation reads as “braking distance is proportional to the square of the speed” - More friction between tires and surfaces, braking distance is less, less friction, more braking distance - When two surfaces make a large amount of friction, the frictional constant will have a low value and same thing vice versa - Braking distance = frictional constant x speed² Total Stopping Distance - ow, we should add the distance the vehicle travels while the driver reacts N - Reaction distance = speed x reaction time - Total stopping distance = reaction distance + braking distance
