Now the Physics… KNOW Your UNITS!!! Mass kilograms (kg) Time seconds (s) Force Newtons (N) which is the same as writing “kg x m/s2” Velocity meters per second (m/s) Acceleration meters per second squared (m/s2)
Now the Physics… Here are the Formulas you get on the FCAT science reference sheet Acceleration (a) a= Change in velocity (m/s) a= vfinal-vinitial Time taken for the change (s) tfinal-tinitial Average Speed (or velocity) (v) v= Distance v= d Time t Force in Newtons (F) F= mass (kg) x acceleration (m/s2) F = ma Work (W) W= Force (N) x distance (m) W = Fd
We can rearrange these equations to get exactly what we are looking for a= vf-vi tf-ti v= d t F = ma W= Fd
So how is the algebra involved in physics? a= vf-vi tf-ti What does the above equation look similar to? m= (y2-y1) (x2 – x1) We use this relationship to solve FCAT physics problems…. Anytime you see a graph with a straight line, you should think SLOPE!
Efficiency and Energy What unit do we use to measure energy? Joules (J) or calorie (cal) Percent efficiency= Energy Output x 100% Energy Input Energy output energy used Energy input energy you started with ***Energy output can NEVER be greater
Other important formulas Potential Energy Stored energy Based on position of object OR arrangement of atoms PE= mass x gravity x height PE=mgh g always = 9.8 m/s2 Kinetic Energy Energy of motion KE= mass x (velcocity) 2 2 KE = m v2 2 Mechanical Energy (ME) ME= PE + KE (super easy!)
Law of Conservation of Energy Energy cannot be created or destroyed…it can only transferred and change form…
Hot object (lots of Energy) cold object (less energy)
Practice Efficiency Problems! Engineers make a battery that supplies iPad2’s with 16,000 J of energy to make an output of 8,000 J of energy in the form of sound and light for the screen. How efficient is the iPad 2?
2. What is the efficiency of a hummer that uses 36,000 J of energy from gasoline to make 27,000 J of kinetic energy to move the car?
3. At Grad bash you ride The Incredible Hulk roller coaster that is 200 meters tall. The roller coaster cart has a mass of 2000kg. At the bottom of the first hill, the speed is 50 m/s. What is the efficiency of the roller coaster assuming it starts from rest at the top of the hill.
4. Hollywood Tower of Terror at MGM boasts that you will be free-falling 120 meters until you reach a speed of 6 m/s near the bottom. How efficient is the ride?
5. You are designing an Avatar roller coaster for Universal. You want to simulate the Toruks, with their deadly swoops and drops. You need to achieve a record speed of 100 m/s at the bottom of the very first drop. You meet with your fellow engineers and determine the efficiency of your sleek Toruk carts is about 85%. How high will the first hill have to be if you wanted to achieve record breaking velocity?
Answers 50% efficiency 75% efficiency About 64% efficiency About 1.5% efficiency About 600 meters high