Aditi Sood - U4 Forces, Motion, PDF

Unit 4 Forces, Motion, Machines, Newton’s Laws – Essential Notes Concept of the AKS What you need to know Reminders AKS: 8a. plan and carry out an investigation and analyze the motion of an object using mathematical and grap...

Unit 4 Forces, Motion, Machines, Newton’s Laws – Essential Notes Concept of the AKS What you need to know Reminders AKS: 8a. plan and carry out an investigation and analyze the motion of an object using mathematical and graphical models (Clarification statement: Mathematical and graphical models could include: distance, displacement, speed, velocity, time, acceleration inertia, force pairs, and free body diagrams.) (GSE SPS8a) MOTION Speed = Distance ÷ Time Units for Speed Speed: m/s, km/hr Velocity Velocity = Distance / Time in a given direction Velocity: m/s South, km/hr down the hallway Acceleration Speeding up, slowing down or changing direction. Acceleration: If the velocity is changing, the object is 𝑉𝑓 − 𝑉𝑖 𝑡 = acceleration accelerating. Units - m/s/s or m/s2 Acceleration = change in speed / time Deceleration = negative acceleration (slowing down) Graphing Motion Graphing of distance vs. time or velocity vs. time can tell you the speed or the acceleration of an object by looking at the slope of the line on the graph. Be careful!!! Be careful! You must check the axes of the graph you are reading to verify what the READ THE AXES!!! graph is telling you about. - Distance / Time Graph Slope of the line in this graph = Speed Distance (Y axis) / Time (X axis) = Speed (slope) - Velocity / Time Graph Slope of the line in this graph = Acceleration Velocity (Y axis) / Time (X axis) = Acceleration (slope) For more help: Check out Stickman Physics Magnitude is another word for size or amount. FORCES Force = any push or a pull. They all have two quantities = Direction and Magnitude Net Force The combination of all forces acting on an object. Any object with a net force > 0 N will be observed as a change in motion. How to calculate Net Force: Applying forces in the same direction. Adding the forces gives you the net force. 125 N + 120 N = 245 N net force = 245 N to the right Applied forces that are in opposite directions. Find the size of the net force by subtracting the smaller force from the bigger force. The direction of the net force is the same as that of the larger force. 120 N - 80 N = 40 N net force = 40N to the left Balanced Forces When the forces on an object produce a net force of 0 N. They are balanced. There is No change in motion. Example: A light hanging from a ceiling. Gravity pulls down on the light while the force of the cord pulls upward. When the forces on an object produce a net force that is not 0 N. They are unbalanced. They will produce a change in motion of an object. Example: Hitting your head on that light will cause it to swing. Or kicking a soccer ball. Free Body Diagrams Free Body Diagrams can help us show the forces acting on an object. We often use a simple rectangle to represent the object no matter the actual shape of the object. By calculating the net force, we can tell whether the object is moving and with how much force. Try these examples. Remember, all forces need a size and a direction. The number in parentheses is the example number. AKS: 8b. construct an explanation based on experimental evidence to support the claims presented in Newton’s three laws of motion (Clarification Statement: Evidence could demonstrate relationships among force, mass, velocity and acceleration.) (GSE SPS8b) Newton’s Laws Newton’s 1st Law of Motion For more help, check out Ducksters.com The first law says that any object in motion will continue to move in the same direction and speed unless forces act on it. It is also known as the Law of Inertia.  More mass means more inertia. It’s harder to get the object with more inertia to change what it’s doing. Newton’s 2nd Law of Motion Second Law of Motion The second law states that the greater the mass of an object, the more force it will take to accelerate the object. Force = mass x acceleration or F=ma. Newton’s 3rd Law of Motion The third law states that for every action, there is an equal and opposite reaction. This means that there are always two forces that are the same. AKS: 8c. analyze and interpret data to identify the relationship between mass and gravitational force for falling objects (Clarification statement: Concepts could include: free fall, terminal velocity, as well as gravity, mass, and weight.) (GSE SPS8c) Gravity (gravitational force) - Force of attraction between objects Matter - Anything that has mass and takes up space The Size of gravitational force depends on - 1.​ Mass of the object (amount of matter in the object) 2.​ Distance between the objects affected by gravity *WEIGHT AND MASS ARE DIFFERENT Weight Mass A measure of gravitational force on an Measured in grams (g) or kilograms object (Kg) Weight is measured using a scale Mass is measured using a balance Measured in Newtons (N) W = mg **Mass does not change --- EVER. Weight = mass x acceleration of gravity *Gravity is always 9.8 m/s/s on Earth…If you leave the planet or get further from the core of the Earth, weight will change. Everything on Earth falls at the same rate - that rate is 9.8 m/s/s. This means that Velocity of Falling Objects for each second the object falls, it increases it’s speed by 9.8 m/s during every second of travel. Air Resistance Air Resistance - Force of air that pushes up on falling objects. Slows down falling objects A force that often works against gravity Dependent on size and shape of object. More surface area means more air resistance. Faster speeds increase the amount of air resistance. Terminal Velocity - Terminal Velocity Air Resistance force = force of Gravity= forces balanced (air resistance and gravity forces balance/are equal) Net force = zero Object is no longer accelerating. Velocity is remaining constant. Direction is … down Yes, they are still falling – just not accelerating (getting faster or getting slower).  Free Fall - Free Fall An object is falling, but Gravity is the ONLY force acting upon it – no particles – no air resistance We do most of our calculations as if things are free falling – we ignore the air resistance. But the only place that this could really happen is in a vacuum, like space. Stuff that’s in orbit in space – is in free fall. AKS: 8d. use mathematics and computational thinking to identify the relationships between work, mechanical advantage, and simple machines, i.e. calculate and give examples of the force-distance trade off that occurs when a machine is used (GSE SPS8d) Work In order for work to be done, in a Physics sense, a force must be applied to an object and the object must move in the direction that the force is applied. Calculating Work We can also calculate the amount of work being done using the formula: W=Fd Force - Distance Trade Off We see the ‘Force - Distance Trade Off’ when we look at the formula. Because Force and Distance are multiplied in order to find work, if we increase one then the other has to be decreased in order to keep work the same. Simple Machines Remember there are 6 simple machines: Machines change the direction or magnitude of the force being used to do work, they DO NOT change the amount of work.  Mechanical Advantage tells us how many times our effort was multiplied because we used a machine to assist us. We need to compare the output of the machine Mechanical Advantage vs. our input into the machine. We can make it a simple ratio and divide. MA = 1 -​ The machine isn’t helping you nor is it making things more difficult. MA < 1 -​ The machine is making things hard for you. It would be easier to NOT use it. MA > 1 -​ The machine is multiplying your input. It is very helpful. -​ For most of our MA practice problems, we’re going to see a machine that would be helping us. We would want to see an MA of 1 or more. That means that an easy way to remember how to set up your math problem is: 𝑏𝑖𝑔 𝑛𝑢𝑚𝑏𝑒𝑟 MA = 𝑙𝑖𝑡𝑡𝑙𝑒 𝑛𝑢𝑚𝑏𝑒𝑟 *this won’t always be the case, but this will work for now until you get a better understanding ​ of work input, input force, work output, and output force.