giosber hartly neelsen
Ronald Gruzinsky
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.
The document describes a pre-lab activity on forces and motion. Students are asked to analyze three scenes where Joe is trying to push a file cabinet across the room. In the first scene, the cabinet does not move when Joe looks at it. In the second scene, the cabinet still does not move when Joe begins pushing. In the third scene, the cabinet begins to slide when Joe pushes it. Students are tasked with identifying the forces acting on the cabinet in each scene and explaining why it moves in the third scene but not the first two. They are also asked how the motion would change if the floor was icy.Read less
All of these forces are measured in newtons (N). As these forces push and pull on objects they affect the motion of the objects. These forces push through some distance in order to do work on a system.
The gravitational force (also referred to simply as gravity) is the force that pulls all the masses in the universe together. All masses attract other masses according to Newton's law of universal gravitation:
The gravitational force acts between all objects that have mass. This force always attracts objects together, and although it is the weakest of the four fundamental forces, gravity has an infinite range. The force of gravity pulls us towards Earth, causing objects to fall. When objects have the ability to fall, that's called gravitational potential energy. Hydropower and tidal power are primary energy sources that take advantage of the gravitational force to generate useful work.
Unless someone is taking very precise measurements in a lab (see for example Cavendish's famous experiment which determined the gravitational constant, G), the force of gravity must include only really big objects (like the sun, the moon or a planet) to be noticeable. The PhET simulation below shows how small gravitational forces are between human sized objects.
The gravitational force is an example of an inverse square law, meaning that the force drops with the square of the distance. This means that if the distance is doubled the gravitational attraction is four times less. Differences in gravitational forces from the moon acting on one side of the Earth, the center, and the other side of the Earth lead to tidal forces.
At cosmological distances (much greater than the size of a galaxy) there is interesting current research on dark energy that shows that a previously unexpected repulsion happens with gravity at long distances, see here).
The University of Colorado has graciously allowed us to use the following PhET simulation. To get a physical intuition about how the law of gravity works, please explore the simulation below. Notice that even the biggest gravitational force below is still quite small compared to how much a person weighs (about 500-1000 N).
The other videos look at the strong nuclear force, weak nuclear force, and electromagnetic force. Check out their youtube channel for more videos like these! (a wonderful resource for curious people).
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