SPEED, TIME AND ACCELERATION Presentation by: M. Hassan Sohail, Yousef hany, Shoaib Sajid, Ajmal Hussain and Ahmed Hissan
Lesson Objectives • To understand what is speed? • To know what are the instruments used to calculate speed? • To use the formula speed=distance/time?
What is speed? Speed is defined as the distance moved per unit time. It can be also defined as the rate at which an object travels from one point to another. The unit for speed is m/s or km/h. The formula to calculate speed is: s=d/t. Now there are two quantities: scalar quantity & vector quantity. Scalar quantity is a physical quantity which has speed but no direction where as the vector quantity is the speed of an object in a particular direction.
What are the instruments used to calculate speed? Many instruments are used to calculate speed: • Doppler radar is what is used by police officer "radar guns" to determine the speed of a motor vehicle. Doppler radar works by sending a beam of electromagnetic radiation waves, tuned to a precise frequency, at a moving object.
Speedometer are generally used in cars are used to determine it’s speed. • Anemometer is a device for measuring wind speed. The device has 3 hollow metal cups that catches the wind and revolves around a rod, the speed is got by the number of revolutions.
Formula speed=distance/time S=d/t, it is the general formula to find the speed. Getting answer is easy; you just substitute the values and you get the answer. Example: If you get a question “A cycle has covered a distance of 10m in 5s. Calculate the speed? So first you substitute the values, s=10/5 so you’ll get the answer as 2m/s. Putting the unit is always important. In case you want to find the distance or time; you can change the subject of formula accordingly.
“Average speed” Average speed is the speed that is usually not constant. Cars stop and go regularly; runners go slower uphill than downhill so we calculate the total speed byaverage speed = total distance traveled/total time it took.
Lesson objectives • To know what are the units of time? • To know the instruments used to calculate time? • To know what is the SI unit of time and how time is used to solve the equations?
What are the units of time? Clocks are used in today’s world to do our tasks at proper time. Time is a system of organization that we use to schedule our lives. Time is made up of seconds, minutes, months, years, etc. Time is a component of the measuring system used to sequence events, to compare the durations of events and the intervals between them, and to quantify the motions of objects. Millisecond, second, minute, hour, day, month, year, decade, century, millenium, eon and light year are the ones I can think of. Other unit measurers are called a pendulum, a stopwatch, a watch, a clock, a water clock, a pocket watch, a grandfather clock, a sundial and an atomic clock.
Instruments used to calculate time Other unit measurers are called a pendulum, a stopwatch, a watch, a clock, a water clock, a pocket watch, a grandfather clock, a sundial and an atomic clock. A watch, clock or chronometer is used to measure the passage of time. A chronometer is an extremely accurate clock. An hour glass can be used for less accurate measurements.
Hour Glass & stopwatch An hourglass (sandglass, sand timer, sand clock, egg timer) measures the passage of a few minutes or an hour of time. It has two connected vertical glass bulbs allowing a regulated trickle of material from the top to the bottom. Once the top bulb is empty, it can be inverted to begin timing again. The name hourglass comes from historically common hour timing. Factors affecting the time measured include the amount of sand, the bulb size, the neck width, and the sand quality. Alternatives to sand are powdered eggshell and powdered marble.
Stopwatch Astopwatch is a handheld timepiece designed to measure the amount of time elapsed from a particular time when activated to when the piece is deactivated.
SI unit of time In 1967 a new SI definition of a second was created based on the radiation from the caesium-133 atom. It is correctly defined as "the duration of 9,192,631,770 periods of the radiation corresponding to the transition between two hyperfine levels of the ground state of the caesium-133 atom." The basic unit of time, was defined as 1/86,400 of a mean solar day or one complete rotation of the earth on its axis.
Lesson objectives • To know what is acceleration and how it is calculated? • To know what is the formula and how to use it in the questions? • To know about the scientist who worked on acceleration? • To know what is positive and negative acceleration?
What is acceleration? Acceleration is the rate of change in the speed of an object, in other words acceleration is the rate at which something speeds up or slows down. The term acceleration is used for an increase in speed; a decrease in speed is called deceleration. A change in the direction of velocity also is an acceleration. Average acceleration is the change in velocity (Δv) divided by the change in time (Δt).Instantaneous acceleration is the acceleration at a specific point in time which is for a very short interval of time as Δt approaches zero.
what is the formula and how to use it in the questions? To determine the rate of acceleration, you use the formula below. The units for acceleration are meters per second per second or m/s2. • Acceleration=Final speed-Beginning speed Time A positive value for acceleration shows speeding up, and negative value for acceleration shows slowing down. Slowing down is also called deceleration. The acceleration formula can be rearranged to solve for other variables such as final speed (v2) and time (t).
Scientist who worked on acceleration Galileo Galileiwas an Italian physicist, mathematician, astronomer, and philosopher who played a major role in the Scientific Revolution. His achievements include improvements to the telescope and consequent astronomical observations. He was curious to know how things fell, when he was younger. He did a lot of research on it. He rolled balls down an inclined plane and found that the speed increased as it rolled down the ramp.
Positive and negative acceleration A constant acceleration produces a straight line or linear slope (rise/run). The slope of a non-linear velocity-time graph (rise/run) will predict an objects instantaneous acceleration. a = v/t
Positive acceleration Negative acceleration
What is Velocity? Velocity – the speed of an object in a direction. Example: An airplane moving North at 500 mph A missile moving towards you at 200 m/s Each time you take a step you are changing the velocity of your body. You are probably most familiar with the velocity changes of a moving bus or car. The rate at which velocity (speed or direction) changes occur is called acceleration. Change in velocity = final – starting velocity velocity
Terminal velocity Force of gravity is constant everywhere. Air resistance increases as you speed up or accelerate.It is not balanced until the force is equal. Equal forces have no acceleration. This constant velocity is called terminal velocity.
“SUMMARY” Speed is defined as the distance moved per unit time. It can be also defined as the rate at which an object travels from one point to another. UNIT IS m/s or km/h Time is a system of organization that we use to schedule our lives. Time is made up of seconds, minutes, months, years, etc. Acceleration is the rate of change in the speed of an object, in other words acceleration is the rate at which something speeds up or slows down. Unit is m/s²
“QUESTIONS” QUESTIONS FROM 1-10
QUESTION # 1&2 1. Q: How far will a car travel in 25 min at 12 m/s? A: 10 km B: 14 km C: 18 km D: 24 km 2. Q: How far will a car travel in 2 hours at 20 m/s? A: 144 km B: 158 km C: 168 km D: 234 km
QUESTION # 3&4 3. Q: Acceleration is the measure of the change in what? A: density B: motion C: velocity D: mass 4. Q: If a car accelerates from 3 m/s to 12 m/s in 3 seconds, what is the car's average acceleration? A: 1 m/s square B: 2 m/s square C: 3 m/s square D: 4 m/s square
QUESTION # 5&6 5. Q: How long does it take to accelerate an object from rest to 15 m/s if the acceleration was 3 m/s square? A: 2 s B: 4 s C: 5 s D: 15 s 6. Q: You started to run at 10 km/h when you left your house and you arrived at school 30 minutes later. Assuming that your average acceleration was 30 km/h square, how fast were you running when you arrived? A: 15 km/h B: 20 km/h C: 25 km/h D: 30 km/h
QUESTION # 7&8 7. Q: How long does it take for a car to change its velocity from 10 m/s to 25 m/s if the acceleration is 5 m/s square? A: 2 s B: 3 s C: 4 s D: 5 s 8. Q: If a car has a constant acceleration of 4 m/s square, starting from rest, how fast is it travelling after 5 seconds? A: 20 m/s square B: 24 m/s square C: 30 m/s square D: 40 m/s square
QUESTION # 9&10 9. Q: If a car has a constant acceleration of 4 m/s square, starting from rest, how far has it travelled by the time it reaches the speed of 40 m/s? A: 50 m B: 100 m C: 200 m D: 400 m 10. Q: If a car accelerated from 5 m/s to 25 m/s in 10 seconds, how far will it travel? A: 100 m B: 150 m C: 200 m D: 250 m