HONORS PHYSICSGood morning! Please…• Take out your homework, to be checked• Answer the warm-up question: • A baseball is thrown straight down from a building that is 65 meters tall. Its initial velocity is 3.0 m/s. What will its velocity be right before it hits the ground?
AGENDA:1. Physics in the News!2. Finish projectile motion activity3. Review4. Review activitiesNOTE: Midterm is Wednesday 9:45-11:45- Bring a book or work to do if you finish the midterm early• LAST DAY FOR HOT TASK/MIDTERM WILL BE WEDNESDAY.• **Cheat sheet update***
MIDTERM TOPICSTopics Suggested Study Techniques1. Conversion, measurement, precision, • Look over all old tests & know how to accuracy do every problem2. One-dimensional motion: constant • Go over your notes from each unit – speed be familiar with concepts3. One-dimensional motion: accelerated • Re-do problems from the homework & motion problems from the review sheet4. Free-fall motion Format:5. Vectors • 30 multiple choice6. Projectile motion • 14 problems with multiple parts7. Forces & Newton’s laws
1.CONVERSION, MEASUREMENT, PRECISION, ACCURACY• Using factor label method to convert numbers• What are some examples of SI units used in physics? English units?• What are the significant figures for the following two numbers: • 0.02003 54300• What is precision? What is accuracy?• How to convert between metric units • Know kilo- to milli-
2 & 3. ONE-DIMENSIONAL MOTION: CONSTANTSPEED & ACCELERATION• Graphing motion • Identifying the information given on an x vs. t, v vs. t, a vs. t graph • Slope of the lines on the graphs • Area under the curve• Solving problems using one-dimensional motion equations
4. FREE-FALL MOTION• The acceleration of an object in free-fall• Using motion equations to solve free-fall problems: • An object dropped from rest • An object dropped with an initial velocity • An object thrown straight up in the air that comes back down.
4. FREE-FALL MOTION• Sample problem: a ball is thrown straight up into the air at 12.0 m/s. • What is the velocity of the ball at its maximum height? What is its acceleration at maximum height? 7.4 m • What is the maximum height that the ball will reach? • What will be the velocity of the ball after 2.0 seconds? -7.6 m/s
5. VECTORS• Difference between scalar and vector quantities • What are some examples of each?• Breaking vector into its components• Solving for resultant vectors by adding or subtracting two vectors
6. PROJECTILE MOTION• Concepts behind projectile motion • Projectile motion is anything that has an initial horizontal velocity that is under the influence of free-fall • X & y dimensions of motion are completely independent of one another • What happens in the x-direction? • What happens in the y-direction?• What is range? At what angle does any object have maximum range?• Problems with initial horizontal velocity• Problems with projectiles launched at an angle.
7. FORCES• Newton’s laws and how they apply in various situations • What is Newton’s first law? Second law? Third?• Drawing free-body diagram• Problems with friction on an inclined plane• Problems with friction on a level surface• Problems with a force applied at an angle• Calculating coefficients of kinetic and static friction.
7. FORCES• A student moves a box of books down the hall by pulling on a rope attached to the box. The student pulls with a force of 185 N at an angle of 25.0 degrees above the horizontal. The box has a mass of 35.0 kg and the coefficient of friction between the box and floor is 0.27. Find the acceleration of the box. -1.2 m/s2
7. FORCES • What is the net force on each object? FN = 10 NFf = 3 N Fa = 5 N Mg = 10 N FN = 10 N FN = 10 N Ff = 3 N Fa = 1 N Ff = 3 N Fa = 3 N Mg = 10 N Mg = 10 N
HOT TASK• What does the normal force do? 4.0 kg• How can we find the normal in both situations shown? 15o 15o
NEWTON’S ACTIVITIES• When a constant force is applied to something, should the speed increase? Should it stay the same? • Use Newton’s Second law and think about the scooter activity – did speed change as force was constant? Did acceleration change?• Explain how Newton’s first law applies in a car when wearing a seatbelt vs. without a seatbelt.
Example: force applied at an angleSuppose a 10.0 kg box is pulled at an angle of 30.0 degrees with a force of 50.0 Newtons. F ¹ mg! Na) Calculate the normal force of the box å FY = 0 ® FN + Fay - Fg = 0 FN + Fay = mg FN = mg - Fay ® (10)(9.8) - 50sin30 FN = 73Na) If the block is accelerating at 1.5 m/s/s, calculate the coefficient of friction. FN Fa = 50 N å Fx = Fnet = ma Fay = 50sin(30) Fax - Ff = ma Ff 30 Fax = 50cos(30) 50 cos30 - m FN = (10)(1.5) mg 43.3- m (73) = 15 m = 0.39
EXAMPLE: FORCE APPLIED AT ANGLE#5 from handout last week:A 120.0 N force is applied at an angle of 45 degrees to a 40.0 kg box. The coefficient offriction between the two surfaces is 0.15. Find(b) The force due to gravity and normal force(c) The force due to friction(d) The acceleration(e) How fast the object is moving in 10.0 sec(f) How far it will move in 10.0 sec
NEWTON’S THIRD LAW
NEWTON’S THIRD LAW“For every action there is an EQUAL and OPPOSITE reaction. • This law focuses on action/reaction pairs (forces) • They NEVER cancel out All you do is SWITCH the wording! •PERSON on WALL •WALL on PERSON
NEWTON’S THIRD LAW• How does this law apply when there is a collision between two objects, like a train and a truck??
NEWTON’S THIRD LAW This figure shows the force during a collision between a truck and a train. You can clearly see the forces are EQUAL and OPPOSITE. To help you understand the law better, look at this situation from the point of view of Newton’s Second Law. Ftruck = Ftrain What about mass & acceleration just after collision? mtruck Atruck = Mtraina trainThere is a balance between the mass and acceleration. One object usuallyhas a LARGE MASS and a SMALL ACCELERATION, while the other has aSMALL MASS (comparatively) and a LARGE ACCELERATION.
N.T.L EXAMPLES Action: HAMMER HITS NAIL Reaction: NAIL HITS HAMMER Action: Earth pulls on YOU Reaction: YOU pull on the earth
NEWTON’S FIRST LAWConcepts Problems• What is it? • What type of problems apply? • An object in motion will remain in motion, or an object at rest will remain at rest unless acted upon 4.0 kg by an unbalanced force.• Fnet = 0 • What conditions can occur? 4.0 kg • Object can be at rest • Object can be in constant motion at a constant speed