Transcript change in speed

Today:
Go over Review Packet from last time
Reviews 3 and 4
Homework: Review Packet
• Elastic potential - Potential energy stored as a result of changing the shape of
an elastic object, such as the stretching of a spring
• Thermal – the kinetic energy of moving atoms or molecules in a substance
• Electric – the kinetic energy of moving electrons
• Electromagnetic – radiant energy that travels in waves
• Nuclear – potential energy stored in the forces that hold the protons and
neutrons together in the center of an atom.
• Chemical – potential energy stored in bonds between atoms
• Translational motion – kinetic energy in an object that is moving from one place
to another
• Rotational motion – kinetic energy of a spinning object
• Sound – kinetic energy of atoms vibrating in bulk
• Gravitational potential – energy stored in an object as it moves away from the
center of Earth
• electrical energy to sound energy: radio playing music
• chemical energy to motion energy: a person running, a battery
powered toy moving
• electromagnetic energy to electrical energy: solar powered device
working
• thermal energy to sound energy: a crackling fire
• What happens to the particles in a substance as the temperature rises?
• Temperature is a measure of thermal energy.
• Thermal energy is the motion of the particles of a substance so if the temperature of a
substance is rising that means the particles are moving faster.
• This causes the particles to collide more often and with more energy so they will get
pushed farther apart from each other.
• As the particles move farther apart, the density of the object decreases.
• Where does most of the energy on Earth come from?
• Radiant energy from the sun
• Trace the energy you got from your breakfast back to the Sun.
• Bacon  chemical energy in the pig’s food  radiant energy from the sun
• Trace the electrical energy in our homes back to the Sun.
• Light bulb  electrical energy in wires  kinetic energy of turbines  kinetic energy of
water (river)  kinetic energy of water moving through the water cycle  radiant
energy of from the sun
• Explain the difference between speed and acceleration.
• Speed is the rate of change of position while acceleration is the rate of change of speed.
• The speed of an object is how its position changes over time while the acceleration is how
its speed changes over time.
• Speed = d/t so its units are distance per time like m/s
• Acceleration = change in speed ÷ change in time so its units are speed per unit time like
m/s/s
• How are mass and weight different?
• Mass is the amount of matter in a substance while weight is the measure of the force of
gravity on an object
• Weight will change if the force of gravity changes but the mass would be the same
• if you go to the moon, you will weigh less because there will be less gravity but your body hasn’t changed
so you still have the same mass
• What are 3 examples of balanced forces?
• Sum of all the forces on an object = zero
• Object is at rest or moving at constant velocity in a straight line
• What are 3 examples of unbalanced forces?
• Sum of all the forces on an object ≠ zero
• Object is accelerating or decelerating or changing direction
• Explain how is air resistance a type of friction?
• Friction is a force that opposes motion because the molecules of different
substances come in contact with each other
• As an object moves through the air, it collides with air molecules and this
interaction opposes motion therefore it is a type of friction
Newton’s Laws of Motion
• 1st law: an object at rest will remain at rest unless acted on by an
unbalanced force. An object in motion continues in motion with the
same speed and in the same direction unless acted upon by an
unbalanced force
• Example: a ball sitting on the floor or a ball flying through the air
(after you release it)
• 2nd law: Acceleration is produced when a force acts on a mass. The
greater the mass (of the object being accelerated) the greater the
amount of force needed (to accelerate the object)
• Kicking a ball is fun, kicking a large rock is not (larger mass requires a larger
force to move it)
• 3rd law: For every action there is an equal and opposite re-action
• The normal force is the force exerted on objects that keep the object
from falling because of gravity
• The normal force only acts on objects that are in contact with a
surface
FN
• An apple on a desk
FG
• A ball rolling down a ramp
FN
FF
FN
FG
FF
FA
• Pushing a grocery cart (the cart is in motion)
FG
• It takes you 65 minutes to walk to school. Your home is 3 miles from school.
Speed = d/t
Speed = 3 mi/65 min
Speed = 0.05 mi/min
• On Monday, it takes your mom 22 minutes to drive to work. On Tuesday it takes
17 minutes. If you live 45 miles from work, how much faster was you mom
driving on Monday compared to Tuesday?
Speed = d/t
2.05 mi/min = 123 mph
Monday Speed = 45 mi/22 min
Monday Speed = 2.05 mi/min
Tuesday Speed = 45 mi/17 min
Tuesday Speed = 2.64 mi/min
2.64 mi/min = 158.4 mph
• A race car accelerates uniformly from 18.5 m/s to 46.1 m/s in 2.47 seconds.
Acceleration = change in speed
change in time
Acceleration = 27.6 m/s
2.47 s
Acceleration = 11.17 m/s/s
• Rocket-powered sleds are used to test the human response to acceleration. If a
rocket-powered sled is accelerated to a speed of 444 m/s in 1.83 seconds what is
its acceleration?
Acceleration = change in speed
change in time
Acceleration = 444 m/s
1.83 s
Acceleration = 242.62 m/s/s
• Graph 1 matches description B because the distance is increasing at a
steady rate.
• Graph 2 matches description a because the distance isn’t changing
over time.
• Graph 3 matches description C because the distance is increasing at
first but over time, the distance isn’t changing as fast