The higher the release point of the ball on the ramp, the faster the ball will be rolling when it reaches the bottom of the ramp because gravity has more time to PULL it down. Repeating a measurement several times and then averaging the results will yield a more reliable result than any single measurement. Main Ideas
Formula: • Speed = Distance/Time • A free rolling object will speed up when rolling down an incline, but its speed will remain nearly constant on a level surface. • When an object rolls down an incline, its speed at the bottom is determined by the height at which the ball was released. Speed
1) Why will the speed of the ball traveling along the level tabletop be the same as the speed of the ball at the bottom of the ramp? 2) Give a reason why the average time, calculated from 5 separate measurements, is more reliable than any single measurement of the time. 3)What effect did increasing the release height have on the speed of the ball? 4) Why do you think the speed of the ball depends upon its release height? Investigation Reflection
Use what you have learned to explain why the water in streams flow swiftly in mountainous areas (like Colorado), but the water in streams in Delaware flows very slowly. Applying What You Learned
Energy is the ability to bring about some kind of change. • Potential Energy (PE) is stored energy. • Ex: Battery • Gravitational Potential Energy (GPE) is energy of position. • Ex: Golf ball waiting to roll down the ramp MAIN IDEAS
Kinetic Energy (KE) is energy of motion. • Ex: Moving golf ball down the ramp and on table top. • A moving object has energy because of its motion thus it gives us an indication of how much a moving object can change the motion of other objects. • The kinetic energy of an object is determined by its speed and mass. • Increasing the size of the speed and/or the mass increases the object’s kinetic energy. • Energy Transfer takes place whenever energy is ‘passed’ from one object to another object. • Ex: From the golf ball to the cards MAIN IDEAS
Energy TransFORMation takes place whenever energy is ‘changed’ from one form to another form of energy. Examples
As the release height of the golf ball is increased, how does the speed of the ball at the bottom of the ramp change? As the release height of the golf ball increases, the speed at the bottom of the ramp also increases.
Based on your graph, what effect does the speed of the golf ball have on the number of cards it knocks down? The greater the speed, the greater the number of cards knocked over by the ball. The greater speed enables the golf ball to create a greater change. (Remember the definition for Energy).
By replacing a solid golf ball with a hollow golf ball and repeating the experiment, what variables changed, and what variables were kept the same? The only variable that changed is the mass of the golf ball. Since gravity speeds up all objects equally, both the solid and hollow golf balls will leave the ramp with approximately the same speed. Everything else was kept “Constant.” Examples???
What effect did changing the mass of the ball (substituting the hollow ball for the solid ball) have on the resulting number of cards knocked down? The hollow golf ball is much less effective at knocking over the index cards. The difference in the solid and hollow balls is their mass. Mass (like speed) is a variable that affects the amount of energy an object possesses.
What was the “change” produced by the ball? The number of cards that were knocked down by the either the solid or the hollow ball.
What factors determine how much kinetic energy (KE) the ball has at any point? Speed and Mass
Applying what you learned Speed limits are a fact of life when driving on roads throughout the state. Various roads/highways have very different speed limits. You will learn in your drivers’ education courses that speed limits are posted for the protection of the driver and passengers in the vehicles, as well as for pedestrians near the roadways. Typical speed limits (in miles per hour) in our state are: 65 mph on Route 1 50 mph on country roads through farmland 35 mph on roads through residential areas 25 mph on roads in busy sections of cities and towns 20 mph for large trucks in sections of cities and towns Use your knowledge of kinetic energy to explain why two speed limits, one for cars and one for large trucks, are needed to help protect the safety of the citizens in Delaware’s cities and towns.
Kinetic energy depends upon both mass and speed, so we can change the amount of kinetic energy by altering the mass, the speed, or a combination of the two factors. It is possible for a large truck, such as a loaded tractor trailer, traveling at 25 mph to have the same kinetic energy as a passenger car traveling at 55 mph. Since the large trucks have a much larger mass, which would give them a much larger kinetic energy, state transportation officials lower their rate of speed. At this lower rate of speed, the energy of the large truck and the passenger car, though traveling 5 mph faster, is much more equitable. Remember that if you have to stop quickly in a vehicle, you must convert your kinetic energy to some other form. The less kinetic energy that the vehicle has to start with, the quicker it can stop.
Thinking about the results of your experiments, identify in which case did the golf ball had the greatest kinetic energy. Consider the entire motion of the golf ball, from its release at the top of the ramp to the point where it comes to rest. At what point in its motion does the ball have its greatest kinetic energy? In the question above, you identified the solid golf ball as having the greatest kinetic energy at the bottom of the ramp. Describe how you could give the hollow golf ball this same amount of kinetic energy. Additional questions to ponder …
The kinetic energy of an object determines the amount of change it can produce in the motion of other objects. The kinetic energy of an object can be transferred to other objects. Objects can have stored energy that is called potential energy. A common form of potential energy is due to the Earth’s gravity. It is called the gravitational potential energy and depends on the object’s mass and how high it is above the ground. Main Ideas FOR INVESTIGATION 3
Energy Transformationoccurs whenever energy changes from one form to another form. The kinetic energy of objects can be transferred to the tiny particles that make up the objects. When this happens, the kinetic energy becomes disorganized and does not contribute to the motion of the objects. Collectively, this random kinetic energy is called heat energy. Main Ideas continued…..
Under the right conditions, the stored energy of an object can transform into kinetic energy, and this kinetic energy can then transform back into stored energy. Whenever an object moves through the air, part of its kinetic energy is transferred to the particles of air. The energy of an object may be transferred to other objects or substances or transformed into types of energy that are difficult to detect, but the energy is never consumed and never disappears. Main ideas: investigation 4
Energy can not be destroyed or created; it only changes from one form to another. Conservation of Energy
All matter is composed of tiny particles. • Particles in a single substance are the same, whether the substance is a solid, liquid or gas. • The particles that make up matter are in constant motion. • The measure of the total motion of all the particles of a substance is called heat energy.
The particles of a solid only vibrate in place. Their connection keeps the particles closely packed together. • The particles of a liquid have more energy and can move by one another. The connections are weaker, but strong enough to keep them close together. • The particles of a gas have the most energy of all. They can move in all directions easily. • States of matter can be changed by adding or removing heat energy.
Adding energy, like heat, causes the particles to move quickly and further apart. • Adding energy will not change the size of the particles, but the total volume will tend to increase as the particles move further away from one another as they vibrate more and more.
The energy of a falling ball is transformed from gravitational potential energy to kinetic energy. When the ball strikes a surface, part of its kinetic energy is transferred to the surface, and as the ball bounces back up, its remaining kinetic energy transforms back into potential energy. main ideas investigation 5
The kinetic energy transferred to the surface takes the form of organized vibrations of the particles that make up the surface. Through these vibrations, the energy is spread to particles throughout the surface. At first, the vibrations of the particles are organized, and produce a wave-like pulse through the solid. Then the particle vibrations become unsynchronized and random. The collective random kinetic energy of the particles is called the heat energy of the substance.
How much energy is transferred during each bounce is determined by the distance the ball drops, the physical properties of the ball and the surface that the ball strikes, and how well the surface is anchored to the floor.
When energy seems to ‘go away’ the ‘missing’ energy is often transferred to particles too small to see, making the energy difficult to detect. Energy chains are useful tools for organizing the description of energy flow in everyday phenomena. Investigation 6: Where is the energy going
Energy changes from one form to another form? The amount of matter in an object? Stored Energy? The ability to bring about some kind of change? The total motion of all the particles of a substance; random disorganized kinetic energy? KE, pe, gpe, energy transfer, energy transformation, energy, speed, mass, weight, height, heat energy, random, conservation of energy
Energy can not be destroyed or created; it only changes from one form to another? Energy is ‘passed’ from one object to another object? Energy of motion? Distance per time? The amount of gravity pulling on an object? KE, pe, gpe, energy transfer, energy transformation, energy, speed, mass, weight, height, heat energy, random, conservation of energy
Energy can be transferred from one object to another. In this transfer process, the energy can be transformed from its original form to a different form. Forces are not energy, but the mechanism by which energy is transferred. The collective random kinetic energy of particles is called heat energy. This form of kinetic energy will not make the object move. Even large quantities of heat energy in an object cannot make the object move. Main ideas for investigation 7
If heat energy is concentrated, the temperature and other properties of the object will noticeably change. Sliding friction is a force that transforms the kinetic energy of objects into heat energy. Main ideas continued
Make an energy chain that describes the flow of energy in this activity. Be sure to note each energy transfer and each energy transformation that takes place. Food energy → (is transformed into) → Kinetic Energy of the arms→ (is transferred to) → the rope → (is transformed into) → heat energy → (and transferred to) → the wooden dowel (some of the heat energy remains in the rope) → (is transferred to) → my fingers & the air
You probably discovered that if the rope slides left and right along the length of the dowel while you are pulling it forward and back, that it was difficult to get either the wood or the ropes to begin to burn. Use the Particle Model to explain why it is important to keep the rope sliding across the same spot on the dowel if you expect the dowel and rope to get hot enough to start burning. When the rope slides along the length of the wooden dowel, the kinetic energy is being transferred to a larger number of particles than it would if the rope moved back and forth over the same spot on the dowel. More particles receive energy, but because the energy is spread over a larger number, each individual particle (on the average) receives less energy. A larger part of the dowel ‘warms up’, but no part of the dowel really gets hot.
When the cup slides to rest in Activity 3, did either the cup or the tabletop get really hot and start smoking? Use what you know about kinetic energy, heat energy and energy transfer to explain your answer. There was no smoking, burning, melting, or any other indication that the objects were getting hot. The main reason for this is that there was very little kinetic energy transformed into heat energy. The gravitational potential energy that is transformed into kinetic energy when the golf ball descends 10 -12 cm is small. When this energy is ultimately converted into heat energy, it is still a small amount of energy. The particles’ kinetic energy will increase, but not by much. The concentration of heat energy must get much greater before we will be able to detect changes in the objects.
Did all of the ropes behave the same in this activity? What differences (if any) did you see, and what could explain these differences? The particles of the cotton rope and the nylon rope both received large amounts of kinetic energy because of the motion of the rope. These concentrations of heat energy produce very different effects in the two ropes. The cotton rope starts to smolder, and snaps because of the weakening effect of the burning process. The nylon rope begins to melt. As it melts, the surface of the rope gets very sticky, making it very difficult to continue to move the rope across the surface of the wooden dowel.