TAKS Objective 5 The student will demonstrate an understanding of motion, forces, and energy.
Speed • Speed is the rate of change in position • V = d t • V = velocity • d = distance • t = time
Set up the Speed Triangle V = d t d v t
Sometimes the question will use the word VELOCITYinstead of speed. v = d t A 1-kilogram ball travels 50 meters in 5 seconds. The velocity of the ball is —
d v t Speed = 56 meters 96 sec Speed = 0.58 m/s Exit 2009
Velocity & Speed • Velocity is the speed and direction of an object • The velocity of an object can change even if the speed remains constant
Acceleration • Acceleration is the rate of change of velocity • Speeding up • Slowing down
Equation to find Acceleration vf - vi a = -------- t vf = final velocity vi = initial (beginning velocity) a = acceleration t = time vf - vi vf - vi a t a
vf - vi a = (30 m/s) – (20 m/s) 2 seconds a = (10 m/s) 2 s a = 5 m/s2 t a Grade 10 2009
What is a force? • Forces are all around us • Pushing • Pulling • Squeezing
Momentum • Momentum can be defined as "mass in motion.” • Momentum depends upon the variables mass and velocity • Momentum = mass x velocity • p = m x v • m = mass • v = velocity • p = momentum p v m
Momentum • Describe the momentum of a 5-kg bowling ball moving westward at 2 m/s. • p = m x v • p = 5 kg x 2 m/s • p = 10 kg x m/ s p m v
p = mv p = 2.0 kg x 15 m/s p = 30 kg • m/s p m v Grade 10 2009
p m v p = m x v p = 0.2 kg x 12 m/s p = 2.4 kg • m/s Exit 2009
ENERGY Energy is the amount of work a physical system is capable of performing. The Law of Conservation of Mass states: Energy can neither be created nor destroyed
A measure of the change a force produces. The work done by a force acting on an object is equal to the force multiplied by the distance through which the force acts. Work W F d
Work is done… …by a force when the object it acts on moves a distance NO work is done by pushing against a wall that will not move. Work IS done throwing a ball because the ball MOVES while being pushed during the throw. Work
The Joule • joule (J) • The SI unit of energy • Amount of work done by a force of one Newton when it acts through a distance of one meter:
A person pushes a large box across a level floor by applying a horizontal force of 200 N. If the person pushes the box a distance of 5 meters in 10 seconds, how much work does the person do on the box? Practice Problem #1 Work =force x distance W=F x d A 2000 joules B 1000 joules C 400 joules D 100 joules W W= (200N)(5m) = 1000 joules F d
The weight lifter used a force of 980 N to raise the barbell over her head in 5.21 seconds. Approximately how much work did she do in raising the barbell? F 380 J G 982 J H 2,000 J J 10,000 J W=F x d W= 980N x 2.04m =1999.2J W F d (Practice problem from TEA released TAKS Test)
The RATE of Doing Work… • Power is the amount of work done in a specified period of time • The more powerful something is, the faster it can do work Power W P t
A mechanic used a hydraulic lift to raise a 12,054 N car 1.89 m above the floor of a garage. It took 4.75 s to raise the car. What was the power output of the lift? A 489W B 1815W C 4796 D 30,294W P=W / t W = F x d W=12,054N x 1.89m = 22,782.06J P= 22,782.06J/4.75s=4,796.2W W P t (Practice problem from TEA released TAKS Test)
Day 2 Newton’s Three Laws, Simple Machines, & Waves
1st Law of Motion (Law of Inertia) An object at rest will stay at rest, and an object in motion will stay in motion, unless acted upon by an unbalanced force.
1st Law • Unless acted upon by an unbalanced force, this golf ball would sit on the tee forever.
What is one type of unbalanced force that acts on an object in motion? Friction!
Friction Slide a book across a table and watch it slide to a rest position. The book comes to a rest because of friction.
Don’t let this be you. Wear seat belts. Because of inertia, objects (including you) resist changes in their motion. When the car going 80 km/hour is stopped by the brick wall, your body keeps moving forward at 80 km/hour. Newton’s 1st Law and You
The force of an object is equal to the product of its mass and acceleration, or F=m x a. 2nd Law
F = m x a 2nd Law
How much force is needed to accelerate a 1400 kilogram car 2 m/sec2? • F = m x a • F = 1400 kg x 2 m/sec2 • 2800 N F 2ndLaw m a
What acceleration will result when a 12 N net force is applied to a 3 kg object? F = m x a a = F = 12 N = 4 m/sec2 m 3 kg F m a Check Your Understanding
2. A net force of 16 N causes a mass to accelerate at a rate of 5 m/s2. Determine the mass. F = m x a m = F = 16 N = 3.2 kg a 5 m/s2 F m a Check Your Understanding
3. How much force is needed to accelerate a 66 kg skier 1 m/sec2? F = m x a F = 66 kg x 1 m/sec2 F m a Check Your Understanding
4. What is the force on a 1000 kg elevator that is falling freely at 9.8 m/sec2? F = m x a F = 1000 kg x 9.8 m/sec2 F = 9800 N F F m m a Check Your Understanding
W = (3 kg•m/s2) x (8.0 m) W = 24 Nm F = (6.0 kg) x (0.50 m/s2) F = 3 kg • m/s2
3rd Law • For every action, there is an equal and opposite reaction.
3rd Law When you sit in your chair, your body exerts a downward force on the chair and the chair exerts an upward force on your body.
The hot gases push down against the ground. As the gases move downward, the rocket moves in the opposite direction, upward. 3rd Law
What is a Simple Machine? • A simple machine has few or no moving parts. • Simple machines make work easier
Wheels and Axles • The axle is a rod that goes through the wheel which allows the wheel to turn • Gears are a form of wheels and axles
Pulleys • Pulley are wheels and axles with a groove around the outside • A pulley needs a rope, chain or belt around the groove to make it do work
Inclined Planes • An inclined plane is a flat surface that is higher on one end • Inclined planes make the work of moving things easier
Wedges • Two inclined planes joined back to back. • Wedges are used to split things.