chapter 5 matter in motion. section 5.1 – measuring motion we have learned all about matter: what...

CHAPTER 5 Matter in Motion

SECTION 5.1 MEASURING MOTION We have learned all about matter: what is it made out of, how it forms, different states Now, we are going to learn about when matter moves Matter moves around you all the time, can you see something moving? Do you know of something that is moving right now? We are going to learn how to measure that movement.

MOTION When you watch something that is in motion, you are always watching the object in reference to another object that appears to stay in place When you are watching the bird fly, it is in reference to the tree below it that is not moving. The object that appears to stay in place is called the reference point. In the example above, the tree is the reference point. Can you give another example?

MOTION An objects change in position relative to a reference point

Motion You can also describe an objects motion with a reference direction, such as north, south, east, west, up or down.

COMMON REFERENCE POINTS The Earth can be used as a common reference point Nonmoving objects such as buildings and trees can also be good reference points A moving object can also be used as a reference point Ex. You are in your car, you see a car zooming past your car, you would be able to tell that the car is accelerating by comparing it to yourself in your car.

SPEED The distance traveled divided by the time interval during which the motion occurred

CALCULATING SPEED The speed depends on how far something traveled and how long it took the object to travel that far. Speed depends on both distance and time Ex. Supposed the balloon took 10s to travel 50m. How far would it have traveled? You divide the distance of the balloon by the time if took (50m)/(10s) = 5m/s You can measure speed in m/s, km/h, ft/s and mi/h

AVERAGE SPEED Most of the time, objects do not travel at constant speeds. Think about when you are in the car, you have stop lights, stop signs and traffic you do not always go the same speed. There is a way to calculated how fast you are going on average You can calculate the average speed by dividing the total distance by the total time Average speed = (total distance)/(total time)

SPEED ON A GRAPH Look at Figure 2 from page 119 The blue line shows the total distance travelled during the trip The distance travelled each hour is different the graph does not cover the same distance each hour for all four hours The distance changes because the speed is not the same throughout the whole trip

AVERAGE SPEED ON A GRAPH You can find the average speed during the 4 hour period by using the average speed equation Average speed = (360km)/(4hours) = 90km/h The red line on figure 2 shows the average speed this line shows the distance increasing by 90km every hour. This line shows that if she travelled 90km/h for 4 hours she would travels 360km and reach her destination right on time The slope of the red line is the average speed

THE DIRECTION THE BIRDS ARE TRAVELLING Imagine that 2 birds leave the same tree at the same time. They both fly at 10km/h for 5 min, 12 km/h for 8 min, and 5km/h for 10 min. Why dont they end up at the same place?

VELOCITY The speed of an object in a particular direction

VELOCITY Velocity is the speed an object is moving AND the direction is it moving. Knowing the velocity helps us know exactly where an object is going. What is the difference between speed and velocity? Speed: how fast an object is moving Velocity: how fast an object is moving AND the direction

SOME ARE TRAVELLING SOUTH, AND SOME NORTH If you look at cars on the highway. You have 2 different directions the cars can travel North and South. If the cars are travelling at the same speed, how are their velocities different?

CHANGING VELOCITY The change of velocity is the change of an objects position Can the velocity change if the speed remains constant? Yes! The direction can change. Can the velocity change if the direction remains constant? Yes! The speed can change.

EXAMPLE If a bus is travelling 15m/s south and changes to 15m/s north, does its speed change? No Does its velocity change? Yes If a bus is travelling 15m/s south and changes to 30m/s south, does its speed change? Yes Does its velocity change? Yes

COMBINING VELOCITIES Since velocity needs speed and direction, there are ways to add and subtract velocities based on the direction If the two velocities have the same direction, you add the speeds. If the two velocities have opposite directions, you subtract the speeds.

COMBINING VELOCITIES Say you are in a bus travelling 15m/s East. Suppose you start walking down the bus at 1m/s West. Are you still traveling at 15m/s? No. What is your new velocity? 15m/s East 1m/s West = 14m/s East Suppose you start walking up the bus at 1m/s East. Are you still travelling 15m/s? No. What is your new velocity? 15m/s East + 1m/s East = 16m/s East

ACCELERATION The rate at which velocity changes over time; an object accelerates if the speed changes, the direction changes, or if both change.

ACCELERATION Unlike normal usage of the word acceleration, in science acceleration is ANY change of velocity. An increase in velocity is called a positive acceleration A decrease in velocity is called a decreased acceleration or a deceleration Acceleration is both how much the velocity changes and how fast the velocity changes. The faster the velocity changes, the greater the acceleration is

CALCULATE AVERAGE ACCELERATION Average acceleration = (final velocity starting velocity)/(time it takes to change velocity) Velocity is expressed in m/s. Acceleration is m/s divided by s which can be expressed as m/(s^2) Look at the drawing on the board. How do you calculate the average acceleration?

ACCELERATION ON A GRAPH When drawing a velocity graph, you have speed on the y-axis and time on the x-axis When drawing an acceleration graph, you have velocity on the y-axis and time on the x-axis Plot the figure on the board on an acceleration graph For the rest of class, work on the data we collected yesterday in lab. What do we need to calculate the speed on the balloons?

ACCELERATION The rate at which velocity changes over time; an object accelerates if the speed changes, the direction changes, or if both change.

VELOCITY The speed of an object in a particular direction

SPEED The distance traveled divided by the time interval during which the motion occurred

DRAW GRAPHS Draw the following graphs. Label the x-axis and the y-axis. Give units and describe what the slope shows. 1. Graph for speed 2. Graph for velocity 3. Graph for acceleration

CIRCULAR MOTION An object travelling in a circular motion is always changing direction. What does that mean for its velocity? What does that mean for its acceleration?

CENTRIPETAL ACCELERATION The acceleration that occurs in circular motion. What are some examples of centripetal acceleration in daily life?

5.2 - WHAT IS A FORCE Use the word force in a sentence So what exactly does force mean?

FORCE A push or pull on an object in order to change the motion of the object; force has size and direction

FORCE A force can change the acceleration of an object How would it change the acceleration? Speed or direction; velocity Any time the motion of an object changes, it is because of force What are some examples of objects changing motion? Scientists measure force in a unit called Newton (N)

FORCES ACTING ON OBJECTS All forces act on objects. For any push to occur, something has to receive the push. You need to have something to push in order for you to exert a force. Can you think of examples of you exerting force on something? Ex. Opening the book, you put a force on the pages Ex.

FORCES ACTING ON OBJECTS Just because you exert a force onto an object, does not mean that the object will move. There are more forces acting on an object and if those forces are greater than the one you are putting onto the object, the object wont necessarily move. Ex. If I try to move the bookcase. I can exert a force, but the force of all of the books and gravity pushing the bookcase to the ground will be stronger than my pushing force, and so the bookcase will not move. Can you think of other examples?

UNSEEN SOURCES AND RECEIVERS OF FORCES It is not always easy to see forces. You cannot always tell which forces are acting on objects There is a magnetic force keeping magnets to refrigerators, but we cannot see it. We also cannot see the force of gravity, but we can see how it works around us

NET FORCE The combination of all the forces acting on an object. The net force shows us which way the object will move, since it is the addition of all of the forces on an object.

DETERMINING NET FORCE When you have 2 forces acting on an object in the same direction, you can add those two forces to determine the net force. The net force will be the addition of the forces and in the same direction of the individual forces. When you have 2 forces acting on an object in opposite directions, you subtract the smaller force from the larger force to find the net force. The direction of the net force will be the same as the direction of the larger force. Examples!

NET FORCE So what does the net force show us? If the net forces are unbalanced, not 0 N, then you know that the object will be moving Balanced forces: the net force equals 0 N The motion of the object will not change; if the object is moving, it will continue to move. If the object is stationary, it will stay stationary. Examples of balanced forces?

NET FORCE Unbalanced forces: the net force does not equal 0 N They produce a change in motion or direction You NEED to have an unbalanced force if the object is moving An object can continue to move even if the force has stopped Ex. Use the golf ball and wooden ball to explain some forces Do worksheet

GRAVITY: A FORCE OF ATTRACTION Watch vacuum video What is going on in that video? Was the result what you were expecting? Why/why not?

GRAVITY A force of attraction between objects that is due to their masses

Since gravity is a force, what can it change about the object? The speed, direction or both!

GRAVITY ON MATTER All matter has mass! Gravity is a result of mass! Therefore, all matter is affected by gravity! This means that all matter has attraction forces to all other matter. This means that you are being pulled, by gravity, towards you pen, the desk, and each other! And they are being pulled towards you. Can you feel it? No. Of course you dont get physically pulled towards your desk. You arent stuck to your desk because the mass of the desk is too small, your mass is also too small to pull the book towards you. HOWEVER, the Earth is big enough to pull you to it!

THE EARTH IS THE BIGGEST THING ON EARTH!! Due to the above statement, of all of the things we will come into contact with on Earth, the Earth is by far the largest. Since gravitation force is related to mass, the Earth has the greatest gravitational force. We are all being pulled towards the Earth. Every time we try to separate ourselves, or another object, from the Earth, we need to use forces!

NEWTON AND THE STUDY OF GRAVITY Why do objects fall towards the Earth? How do the planets keep in their orbit? These two questions are related! Newton was the first person to document how these two are related The legend is that he came up with the answer to both questions by tossing an apple and watching it fall back to Earth. We know that unbalanced forces cause things to move. What is the force that causes the apple to fall and the force that keeps the moon moving around the Earth are the same! Gravity!

THE LAW OF UNIVERSAL GRAVITATION All objects in the universe attract each other through gravitational force. The size of the force depends on the masses of the objects and the distance between the objects. This law can be understood in 2 parts: Part 1: Gravitational force increases as mass increases Part 2: Gravitational force decreases as distance increases

GRAVITATIONAL FORCE INCREASES AS MASS INCREASES Think of an elephant and a cat. The elephant is so much larger that the cat, which means it has a greater gravitational pull to the Earth, which is why it is harder to pick up an elephant than a cat. Since both the elephant and the cat have mass, they also have a pull towards each other. However, since the Earth is so big in comparison, you cannot see that force. In the same way, when an astronaut is on the moon, they are able to jump and move easier because the moon has less mass than the Earth, and so there is less gravitational pull on the astronauts.

GRAVITATIONAL FORCE DECREASES AS DISTANCE INCREASES Why doesnt the giant sun pull you towards itself more than the Earth pulls us to it? The answer lies in the fact that the sun is so far away! We are about 150million km from the sun. Due to this distance, the gravitational force is very small. If we were to stand on the Sun, the gravitational pull would be so great due to the Suns size, that we would not be able to move. It is the gravitational pull from the Sun on the Earth that keeps the Earth in orbit. This gravitational pull on the planets is large because of the mass of both the Sun and the Earth.

MASS A measure of the amount of matter in an object

WEIGHT A measure of the gravitational force exerted on an object; its value can change with the location of the object in the universe

WEIGHT Mass does not change whether you are on Earth or the Moon or the Sun Weight will change in each of these different places. As long as the gravitational pull remains the same, mass and weight can be used interchangeably. If you moved to somewhere with greater gravitational pull, the weight will greatly increase, but the mass would remain the same. Look at Figure 6 on page 139

UNITS OF WEIGHT AND MASS Force Newton (N) Weight is the measure of gravitational force Newton (N) Mass grams (g) 100g = 1N When you stand on a scale, you measure the gravitational force between you and the Earth. So it should be measured in Newtons. However, it is normally expressed in colloquial terms, pounds or kilograms.

chapter 5 matter in motion. section 5.1 – measuring motion we have learned all about matter: what...

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