FORCES OF MOTION Georgia Shared Resources

STANDARDS

MOTION  In order to describe the motion of an object, you must first be able to describe its position—where it is at any particular time.  More precisely, you need to specify its position relative to a convenient reference frame.  If your car is moving in the same direction and same speed as the bus, the bus will appear to not move with respect to you. Of course, if you compare the speed with the ground, both of you will be moving at some velocity.  Watch the Speed, Velocity and Acceleration

SPEED VS. VELOCITY  Speed refers to how fast an object is moving in terms of distance moved and time taken to move in.  Velocity is a measure of speed in a given direction. Velocity is important in that it distinguishes the direction the object is traveling.  In physics, we use velocity because when comparing different object's motion it is important to know not only the magnitude but also the direction of the motion.  Velocity equals the change in displacement of distance divided by the change in time.

SPEED VS. VELOCITY ** CD pg. 15 & 16 Velocity Practice Problems

DISTANCE VS. TIME GRAPHS 1. Watch the videos on pg. 4 of Module and fill in guided notes. 2. CD pg. 19 Graphing Distance vs. Time

ACCELERATION  Acceleration is not just speeding up. It is any change in velocity: speeding up, slowing down, or changing direction.  CD pg. 17 Acceleration Calculations

FORCES: WHAT IS A FORCE?  A force is simply a push or a pull.  can cause a change in motion  a vector quantity, meaning that it has both magnitude (size or numerical value) and direction.  Example: a game of tug-of-war  When each team is pulling with an equal force in opposite directions, then neither team can cause the other team to move. Forces that are equal in size, but in opposite directions are called balanced forces. Balanced forces do not cause a change in motion.

FORCES: WHAT IS A FORCE?  if one team is able to pull with a greater force than the other team, the there will be a change in motion.  Forces that cause a change in motion are called unbalanced forces.  Unbalanced forces can occur in the same direction or in opposite directions. Unbalanced forces are not equal and opposite.  More than one force can act on an object at one time.  Looking back to the game of tug of war, each team member experiences the applied force of the other people in the game as well as the force of gravity holding them to the ground.  The combination of all of the forces acting on an object is the net force.  The net force determines the motion of the object. For balanced forces, the net force is zero indicating that there is no motion.

FORCES: WHAT IS A FORCE?  When more than one force is acting on an object, forces that are in the same direction are added together and forces in opposite directions are subtracted.  Example 1:  Suppose you and a friend need to move a piano. To do this, you push on one end and your friend pulls on the other end. Your added forces are enough to move the piano. This is because your forces are in the same direction.  Example 2:  Consider two dogs playing tug of war. Since the dogs are pulling in opposite directions, the forces are subtracted. The net force is the difference between the two forces in the direction of the larger force.

FORCES: WHAT IS A FORCE? Watch the videos at the bottom of pg. 7 of the module. Then, determine if the force is balanced or unbalanced.

TYPES OF FORCES  All forces can be placed into two basic categories: distant forces and contact forces.  Contact forces are those forces in which the interacting objects have some sort of physical contact.  Distant forces, on the other hand, are those forces in which the two interacting objects do not have physical contact but are still pushing or pulling on each other at a distance.

TYPES OF FORCES

TYPES OF FORCES: MORE CONTACT FORCES

FREE BODY DIAGRAMS Go to pg. 9 of the module. You will watch some videos about free body diagrams and record notes as needed. Then, play the interactive game at the bottom of the page for practice.

GRAVITATIONAL FORCES  Every object in the universe attracts every other object in the universe.  The force of gravity is dependent on both the mass of the object and the distance between the objects.  The more massive the objects the more gravitational force each will experience. In addition, the closer the objects are to each other the more gravity they will experience.

ACCELERATION DUE TO GRAVITY  The higher any object starts falling from above Earth's surface, the faster it's traveling by the time it reaches the ground.  When objects fall to the ground, gravity causes them to accelerate.  Gravity causes an object to fall toward the ground at a faster and faster velocity the longer the object falls.  In fact, its velocity increases by 9.8 m/s 2, so by 1 second after an object starts falling, its velocity is 9.8 m/s.  By 2 seconds after it starts falling, its velocity is 19.6 m/s (9.8 m/s m/s), and so on.  in the absence of air resistance, all objects fall with the same acceleration (which is denoted by a constant g).

ACCELERATION DUE TO GRAVITY Knowing the gravitational acceleration constant and the mass of the object can provide us with the weight. To calculate weight, the following equation is used: w = m x g (On Earth, the gravitational constant (g) is 9.8 m/s 2 )

NEWTON’S LAWS OF MOTION Go to pg. 11 of the module and watch the video about Newton’s Laws of Motion. Be sure to use the guided notes as you watch. Then, complete the Newton’s Laws of Motion WebQuest. **More information regarding Newton’s Laws can be found on pgs of the module.

WORK  The scientific definition of work differs from its everyday meaning.  Certain things we think of as hard work, such as writing an exam or carrying a heavy load on level ground, are not work as defined by a scientist.  The scientific definition of work looks at the force exerted on an object and the distance the object moves.  In order to do work the force applied to an object must be in the same direction as the movement of the object and the object must move a certain distance.  Therefore, if the object does not move then no matter how much force is exerted; no work has been done.

WORK We can mathematically solve to see how much work has been done. The equation for work is as follows: W = F * d

WORK Complete practice problems 1-6 at the bottom of pg. 15 in the module. Be sure to show your work.

MECHANICAL ADVANTAGE  Simple Machines make work easier by multiplying your effort force or by changing the direction of the effort force.  Be familiar with the 6 simple machines:

MECHANICAL ADVANTAGE  Mechanical advantage is a numerical value that indicates how beneficial it is for you to use the machine.  provides the ratio of resistance to effort force magnitudes for any simple machine.  The higher the mechanical advantage means the more the machine multiples the effort force.  If the mechanical advantage is less than one it means that you are having to exert more force than if you were not to use the machine, but you have to exert the force over less distance.  The total amount of work is the same regardless of if you use the simple machine or not.

MECHANICAL ADVANTAGE

 Mechanical advantage means putting a smaller force into a simple machine to output a larger one.  gives us a little less extra output than we would expect.  This is because factors such as friction and machine wear over time and cause a loss of energy.  Actual mechanical advantage takes these factors into account, while ideal mechanical advantage does not.

MECHANICAL ADVANTAGE  The force applied to a simple machine is called the effort force, Fe.  The force exerted by the machine is called the resistance force, Fr.  The resistance force is the load or the weight of the object being moved.  The distance in which the effort force is applied over is called the effort distance, d e.  The distance in which the resistance of the object moves is called the resistance distance, d r.  The value for mechanical advantage unitless.

MECHANICAL ADVANTAGE

Complete practice problems 1-6 on pg. 16 of the module. Make sure to check your answers.