Phet.colorado.edu Forces
Patrizia Leones
What would you learn if you could turn off the atmosphere? What problems might you solve if you could increase the force of gravity or had the ability to manipulate individual electrons in a circuit? Demonstrations and experiments have long been an important tool in science education, yet real-world limitations often make it impossible for students to see invisible interactions or understand the influence of massive forces. But by using PhET, an interactive simulation platform developed at CU Boulder, students can alter powerful forces and see the unseen.
Because these games have the potential to be distracting, PhET researchers conduct extensive testing on new projects. Each simulation is analyzed carefully to make certain that students are learning the intended concepts and can easily interact with the software. Researchers observe which features are helpful and which are distracting, eliminating superfluous elements and adding new details that aid learning.
Explore the forces at work when pulling against a cart, and pushing a refrigerator, crate, or person. Create an applied force and see how it makes objects move. Change friction and see how it affects the motion of objects.
Identify when forces are balanced vs unbalanced.
Determine the sum of forces (net force) on an object with more than one force on it.
Predict the motion of an object with zero net force.
Predict the direction of motion given a combination of forces.
This investigation allows us to better understand the principles of forces and motion, and how they are related to the angle of a ramp. It also helps us make predictions and draw conclusions based on our observations and data.
The concepts learned in this lab can be applied to real-life situations such as designing ramps for wheelchairs or skateboards, understanding the motion of objects on inclined planes, and predicting the speed and distance of objects rolling down hills or mountains.
This simulation scaffolds the main concepts of forces and motion through 4 different screens: Net Force and Motion, The Basics of Motion, Friction, and finally Acceleration. On the first screen, students can place pullers on either side of a massive cart, set up an experiment, and test to see what happens with balanced or unbalanced forces. The sim incorporates the representation of vectors to visualize the size of the forces on either side of the cart, so students can see that various situations can lead to balanced or unbalanced forces, and that when a net force is applied the cart accelerates in the direction of the net force. The subsequent screens show a robotic pusher that can apply a pushing force to various objects. On the Motion screen, objects of varying masses are placed on a skateboard so friction can be neglected when considering the motion of the objects. On the Friction screen, a slider is introduced that allows the student to adjust the coefficient of friction, and see the effect on motion. Finally, the acceleration screen introduces an acceleration meter and a bucket of water, providing a visual representation of acceleration in a real-world context.
PhET simulations are most often compared to Gizmos from Explore Learning, although our design philosophy is a bit different. We try to make extremely flexible tools with intuitive interfaces that allow the simulations to be used in multiple modalities.
Learners will discover that there are two main categories of forces, namely contact and non-contact forces. They will be introduced to the concept of force fields. This chapter has many opportunities for getting the learners to engage physically with the concepts. Have learners pull and push objects and move each other around the classroom or outside in the school grounds. Have them push against buildings to experience the resistance offered by surfaces. Allow them to walk on different surfaces and feel the effects of friction.
There are many tasks included in this chapter. You might not have time to cover all of them. Some are extension tasks and some tasks are revision from Gr. 7 and 8. You will need to assess the requirements and capabilities of your class in order to decide which tasks to perform. There is a lot of content to cover in this chapter and many concepts form the foundation for what learners will cover in Physical Sciences in Gr. 10-12. You might need to spend more than the allocated 2 weeks of time that is specified in CAPS. Some of the other chapters in this term might not require as much time.
Did you know that these workbooks were created at Siyavula with the input from many contributors and volunteers? Just turn to the front to see the long list! Read more about Siyavula at our website:[link]www.siyavula.com. You can also sign up at our community page if you would like to stay in touch and get involved in our projects.
Siyavula has also created a range of textbooks for other grades and subjects, and we are going to be producing more. These textbooks and workbooks are openly-licensed and freely available for you to use, download, copy, rework and redistribute. The Siyavula textbooks that are currently available are:
Think of the following situation: You are all helping your teacher to rearrange the classroom and she asks you to move her desk from one side of the classroom to the other. How would you do that? The desk is too heavy for you to lift, so how do you get it across the classroom?
A force is a push or a pull on an object. The unit in which we measure force is a newton (N). It is named after Sir Isaac Newton, an English physicist and mathematician. Sir Isaac Newton is recognised as one of the most influential scientists of all times. The unit of force is named after him in recognition of his work in mechanics and his three laws of motion.
In 1687, Newton published Philosoph Naturalis Principia Mathematica, which is often thought of as one of the most important books in the history of science. In it he describes universal gravitation and the three laws of motion.
We use forces every day of our lives. Our own bodies rely on forces. Our muscles pull on our bones to allow us to move. Our feet push on the ground when we walk. To open doors, to pick up our food - everything we do involves some kind of force.
This activity is all about experimenting with different objects and seeing what happens to them when we push and pull them. Learners should see that pushing on solid objects accelerates them. Pushing or pulling on sponges, balloons and play dough distorts their shape and the ball can be made to move. Each group will need the materials listed below.
When one of you pushes the ball to the other, the third person must give the ball another push at an angle to the direction in which it is already moving. What were you able to do to the direction in which the ball was moving?
Pick up the piece of putty or play dough. Exert pulling or pushing forces on it. Try this out with the blown up balloon too. What are you doing to the shape of the putty or play dough and the blown up balloon?
Exerting forces on the putty or playdough changes its shape and it remains deformed. Exerting forces on the balloon also changes its shape, but it resumes its shape again once you stop exerting a force on it.
Forces can change the motion of an object. If an object is stationary, a force can cause the object to start moving. Or, if an object is already moving, a force can cause an object to speed up or slow down.
How do we describe the motion of an object? When an object is moving, we say it has a velocity. Velocity is the rate of change of the position of an object. Velocity is the speed of an object and the direction in which it is moving. Speed describes only how fast an object is moving, whereas velocity gives both how fast and in what direction the object is moving.
An object can move at constant velocity. This means it travels at the same speed in the same direction. For example a car travelling along the highway at 100 km/h in a straight line has a constant velocity. However, what happens when the car moves faster or slows down?
We saw in the last activity that we could change the motion of an object by applying a force to make it speed up or slow down. The velocity of the object is changing over time due to a force acting on it. This is called acceleration. Acceleration is the rate of change of a body's velocity with time. In other words, it is a measure of how an object's speed changes every second.
What we saw in the last activity is that whenever one object exerts a force on a second object, the second object exerts a force back on the first object. You saw this when you pushed against a wall. We say that forces act in pairs. Newton called the one force the action, and the other force the reaction, as shown in the following diagram.
We also saw that when you exerted a force on the wall, you experienced the wall exerting a force back on you. Forces act in pairs on different objects. The force exerted by the second object is equal in strength and opposite in direction to the first force.
What we have described here is actually Newton's Third Law of Motion. The law states that when one body exerts a force on a second body, the second body simultaneously exerts a force equal in strength and opposite in direction to that of the first body.
If you take Physical Sciences in Gr. 10-12, you will study Newton's laws in more detail in Gr. 11. You will see how these three laws laid the foundation for classical mechanics, one of the oldest and largest subjects in science, engineering and technology.
In the last activity, we also saw that more than one force can act on an object at the same time. For example, when two of you were pushing or pulling on your friend in the middle. The effect of the different forces acting together depends on how big each force is and what direction each force is acting in. When two or more forces act on an object, then the forces combine to make a net (overall) force.
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