Unit 2- Forces covers Newton's laws of motion, different kinds of forces, and problems that tie the constant acceleration model to different forces.
Newton's 1st law states that an object at rest will stay at rest and an object in motion will stay in motion unless acted upon by an unbalanced force, meaning that an object will change its velocity only when the forces acting upon it are unbalanced. For example, a hockey puck sliding along the ice without friction will continue to slide at a constant velocity until it encounters an unbalanced force, like when it hits the side of the rink.
Newton's 2nd law goes into more detail relating net force, mass, and acceleration of an object, stating that mass and acceleration are inversely proportional and force and acceleration are proportional. because the unit of force, the Newton, is derived from meters, seconds, and kilograms, the relationship between net force, mass, and acceleration can be written as F=ma or a=F/m. Examples of problems with Newton's 2nd law could be:
A 10 kg object requires how much force to accelerate at 100m/s/s?
F=10kg*100m/s
F=1000N
Newton's 3rd law states that for every force there is an equal and opposing force. For example, The earth exerts a gravitational force on the moon, making it orbit around the earth, and the moon exerts a force on the Earth, creating tides. These to forces are in fact equal, as the force is really between the moon and the Earth. The moon only moves more because it has less mass, and can accelerate more according to Newton's 2nd law.
Forces can be represented in different ways, including system schemas and force diagrams. A system schema relates all of the different objects in a system and identifies the forces between them, and a force diagram identifies the different forces acting on a single object and their directions.
Newton's 1st law states that an object at rest will stay at rest and an object in motion will stay in motion unless acted upon by an unbalanced force, meaning that an object will change its velocity only when the forces acting upon it are unbalanced. For example, a hockey puck sliding along the ice without friction will continue to slide at a constant velocity until it encounters an unbalanced force, like when it hits the side of the rink.
Newton's 2nd law goes into more detail relating net force, mass, and acceleration of an object, stating that mass and acceleration are inversely proportional and force and acceleration are proportional. because the unit of force, the Newton, is derived from meters, seconds, and kilograms, the relationship between net force, mass, and acceleration can be written as F=ma or a=F/m. Examples of problems with Newton's 2nd law could be:
A 10 kg object requires how much force to accelerate at 100m/s/s?
F=10kg*100m/s
F=1000N
Newton's 3rd law states that for every force there is an equal and opposing force. For example, The earth exerts a gravitational force on the moon, making it orbit around the earth, and the moon exerts a force on the Earth, creating tides. These to forces are in fact equal, as the force is really between the moon and the Earth. The moon only moves more because it has less mass, and can accelerate more according to Newton's 2nd law.
Forces can be represented in different ways, including system schemas and force diagrams. A system schema relates all of the different objects in a system and identifies the forces between them, and a force diagram identifies the different forces acting on a single object and their directions.
This system schema identifies three objects in the system, a book, a table, and the Earth. Focusing on the book, there is a gravitational force between the book and the Earth, a normal force between the book and the table, and a frictional force between the book and the table.
While a box representing the book and an arbitrary angle of 30 degrees have been included, a force diagram only needs a point representing the object and force vectors drawn from the point representing each force. It is also helpful to label each force, Force of something by something on something.
Working with forces is like working with vectors, as both have a direction and magnitude. To add forces, you can use the tip-to-tail method of adding the vectors. If the forces are pointing in the opposite direction, it is as simple as subtracting their magnitudes. For example, an object with a 150N applied force to the right and a 100N frictional force to the left will have a net force of 50N to the right.
We can use this net force to relate forces and acceleration with Newton's 2nd law. For example, if the object with a 50N net force to the right has a mass of 100kg, it will accelerate at 0.5 m/s/s:
a=F/m
a=50N/100kg
a=0.5m/s/s
Using acceleration, we can calculate different aspects of the object's motion using kinematic equations.
Working with forces is like working with vectors, as both have a direction and magnitude. To add forces, you can use the tip-to-tail method of adding the vectors. If the forces are pointing in the opposite direction, it is as simple as subtracting their magnitudes. For example, an object with a 150N applied force to the right and a 100N frictional force to the left will have a net force of 50N to the right.
We can use this net force to relate forces and acceleration with Newton's 2nd law. For example, if the object with a 50N net force to the right has a mass of 100kg, it will accelerate at 0.5 m/s/s:
a=F/m
a=50N/100kg
a=0.5m/s/s
Using acceleration, we can calculate different aspects of the object's motion using kinematic equations.
https://www.youtube.com/watch?v=Ee6CHn0MRKE
Other examples of problems with forces and kinematics include different motion models, like motion maps.
The upper motion maps is a constant velocity model, which means that the forces acting on the little car must be balanced. However, in the lower motion map, the little car is accelerating to the right, so there must be some net force on the car to the right to cause the acceleration.
Widget is loading comments...