An Introduction To Physics. Physics is the study of the relationships between matter and energy.
Physics deals with the interactions of matter and energy, both PE vs KE!!!!
Newtonian Physics • Named for Sir Isaac Newton, it deals mainly with the interactions of visible objects around us • Physics explains the universe in mathematical terms.
Motion MOTION: a change in position, measured by distance (also called DISPLACEMENT) and time.
SPEED!!!! (one more thing) • Instantaneous Speed: the rate of speed at any particular moment in time • What device measures instantaneous speed on you car???
Here’s a problem (or two)….. • If the earth spins on its axis at 1100 miles/hour, what is the speed of the Earth's rotation in feet per second? • The earth travels at 68,000 miles/hour as it moves around the sun. How many miles does the earth travel in one trip around the sun?
Speed • Speed = Distance time s = d t Example: A car travels 450km in 5 hours. What is the speed of the car?
Answer: • Speed = distance time • Speed = 450 Km 5 hours • Speed = 90km hr
More practice • 1. How far can a plane travel if it flies 800km/hr for 9 hours? • 2. How long does it take a ship to go 500 km if it travels at a speed of 50km/hr?
Answer If: s = d t Then: d = s t 800km 9hr = 7200km = hr 7000 km
Answer And then: since s = d t t = d s 500km 1hr = 10hrs 50km
Average Speed • Average speed: the speed of moving objects is not always constant: • Average speed = total distance total time
MORE SPEED!!!! • Average Speed Practice Problem: You drive 300 kilometers in 3 hours before stopping for 30 minutes for lunch and gas. After lunch you travel 150 kilometers in an hour and a half. What was your average speed for the trip?
Average speed= Total Distance Total Time =300km + 150km 3 hr +.5 + 1.5hrs 450km = 90km 5hr hr
Velocity • Speed in a given direction. • What is the velocity of a boat that travels from St. Peter to Mankato (10 miles) in 15 minutes?
Answer • Speed = distance = 10miles time 15min • Speed = 0.6666667 mi = .7 mi min min
Change your answer to mi/hr! • 0.67mi 60min = min hr • 40 mi hr
Distance-time graphs • On your paper, graph the following: • Time Sec Distance m 0 0 5 7 10 14 15 21
SPEED Distance (m) time (sec)
Distance - Time Graph: • Time is the independent variable and always plotted on the horizontal axis.Distance is the dependent variable and always plotted on the vertical axis.The slope of this line indicates the speed.
Was your graph a straight line? • A distance-time graph which is a straight line indicates constant speed. • In constant speed, the object does not speed up or slow down. The acceleration is zero.
REFERENCE POINT • Reference point: • the point from which movement is determined, and which is assumed to be nonmoving itself.
What is motion? • If you are standing in one place, and your friend walks by you, are you moving relative to your friend? • Is your friend moving relative to you? • Is either of you moving relative to the earth?
Answer: • You are moving relative to your friend, and your friend is moving relative to you! • You (the Joker) are not moving relative to the earth, but your friend is. You are both moving relative to the sun! Who is moving relative to the computer screen?
What is motion? • If you and your friend are walking down the hall together at the same speed, in the same direction, are you moving relative to your friend? • Is your friend moving relative to you? • Are either of you moving relative to the earth?
Answer: • You are NOT moving relative to your friend, and your friend is NOT moving relative to you. You both are moving relative to the earth.
Frame of REFERENCE • EXAMPLE: Tossing a ball • Describe the motion of the ball. • "If we were going down the road in a school bus, me standing in the isle and you sitting in the seats, would the motion of the ball be different?" • "If someone was standing beside the road as we passed, and imagine that the bus was TRANSPARENT……what would they see the ball doing?"
Frames of Reference To measure movement, some point must be considered as nonmoving. • Most common is the earth • Motion is a change in position,relative to a frame of reference
Earth is the most common frame of reference, however: • Earth rotates on its axis at almost 1100 miles/hour. • Earth moves around the sun at over 68,000 miles/hour. • The whole galaxy is rotating at about 490,000 miles/hour. • Is there a universal frame of reference we can use to define the motions of all things?
VELOCITY -- speed in a given direction. • Speed only gives distance and time. • Velocity gives distance, time, and the direction of travel.
Displacement and Velocity Scalar: a quantity that has only magnitude or size. There is no direction. For example: 100 kg, 5 m Or 6 ml. Vector: a quantity having both magnitude and direction For example: 7 km North (magnitude of 7, direction is North)
Velocity is known as a vector quantity because it has both speed and direction. Consider the flight of an airplane: The first arrow (“A arrow”) shows the speed and heading of the plane. The second arrow (“Another arrow”) shows the speed and direction the wind is blowing. Since the wind is changing the speed and direction of the plane, the two vectors are added, head to tail, to determine the actual speed and direction traveled. If the length of the blue vectors is drawn to scale, the length of the resultant vector will indicate the actual velocity of the plane. When you go around a curve at a Constant speed, are you changing Direction???
More VELOCITY NOTES • Constant Velocity = constant speed and constant direction ( the object is moving in a straight path) • Changing velocity means either a decrease or increase in speed, motion along a curved path, or both • Cars have 3 controls to change velocity: • 1) gas pedal 2) brake 3) steering wheel
VELOCITY…..still • Average V = (Vi + Vf) 2 • Vi = initial velocity • Vf = final velocity • You release your mousetrap car and it’s final velocity is 2 meters 1sec What is its average velocity? 0 m + 2 m 1 s s 2
ACCELERATION • Acceleration:The rate of change in velocity. • Acceleration = Vf –Vi 1 t • kmf – kmi 1 hr hr hr
ACCELERATION • Problem: A car is moving in a straight line it speed up from 65km/hr to 74km/hr, in .17hrs What is the car’s acceleration. • Acceleration = Vf –Vi 1 t 74kmf – 65kmi 1 = hr hr 0 .17hr 53 km/hr2
ACCELERATION!!! • Problem: Suppose a car moving in a straight line steadily increases its speed each second. First from 35 to 40 km/hr, then from 45 to 50 km/hr. What is its acceleration?
15km 1h 1min 1 = .001 km • hr 60 min 60 sec 3 sec2
ACCELERATION!!! • Problem 2: In 5 seconds a car moving in a straight line increases its speed from 50 km/h to 65 km/h while a truck goes from rest to 15 km/h in a straight line Which undergoes greater acceleration? What is the acceleration of each vehicle?
Both undergo the same acceleration 15km 1hr 1min 1 = .00083km/s2 hr 60min 60 sec 5 sec
ACCELERATION!!! • Acceleration also applies to changes in direction • EX: going around a curve at a constant speed of 50 km/hr, what do you notice or feel? • motion is changing every instant because velocity is changing every instant • YOU ARE ACCELERATING!!!!
ACCELERATION • Deceleration ( “negative” acceleration): • A term commonly used to mean a decrease in speed. • Acceleration in a direction opposite to the direction of travel. • Deceleration is negative acceleration and has a negative value to indicate direction.
Graph the following on a distance-time graph: • Time (s) Distance (m) 0 0 1 5 2 20 3 45 4 80 5 125
Distance (m) 0 1 2 3 4 5 time (sec)
Was your graph a curve? • A graph that curves on a distance-time graph shows that the object is accelerating • A graph of acceleration, always has shape!!
Graphs are an excellent tool for analyzing patterns of motion and determining whether the motion is uniform or non-uniform. Position time graphs can determine whether the motion is uniform or non-uniform. The slope of a position time graph represents the velocity. If a graph consists of a straight line, the slope is constant
A constant slope means, a constant velocity, therefore we have uniform motion
The slope of the line can be found using the following formula Or simply put
Velocity vs Time Graphs If Miss. Piggy spent 3 hrs rowing her rubber canoe along the Nile River at an average speed of 5 km/hr. Question: What is the total distance traveled by Miss. Piggy? V = d 3hrs 5km t hr Sketch a p/t and a v/t graph of the data