Force/Work/Energy

Force

-A force is a push or pull that has both magnitude (amount of force) and direction.

- Net force- two or more forces acting on an object. Ex.

  • 25N force to the right + 20N force to the right = 45 N force to the right
  • 25N force to the right – 20N force to the left = 5 N force to the right

-Forces are either balanced (equal, no movement occurs) or unbalanced (unequal, movement occurs)

Gravitational Force

-Always constant on earth

-The force of attraction between two objects (think of magnets)

-Depends on the mass of objects and the distance between them

Friction Force

-Friction is a force that opposes motion when two objects touch.

-Types of friction:

  • Static Friction - no movement occurs but objects are touching
  • Fluid Friction – occurs in water ( i.e. swimming) and in air (air resistance)
  • Sliding Friction – occurs when two objects slide against each other
  • Rolling Friction – occurs when one object rolls over another

Inertia

-The tendency of an object at rest to resist motion

-Also, the tendency of an object in motion to resist any change in its motion

-Inertia is the force that must be overcome to make something move

-Inertia is also the force that must be overcome to make something stop or slow down.

Mass vs. Weight

-Mass is the amount of matter in an object. It is constant… it does not change

-Weight is a measure of gravitational pull on an object. It changes because gravity changes. Ex. On the moon you are the same size (mass) yet you will weigh less because there is less gravity or gravitational pull on the moon

Work

-Work is defined as the measure of a force acting over a distance. Ex. John threw the ball with a force of 50N over a distance of 25 meters.

-Work only occurs when both conditions below are met…

  • An object moves because of a force
  • An object moves in theSAME direction as the force applied

Machines

-Machines make work easier by changing the magnitude (amount) of a force and/or the distance over which a force is applied.

  • The longer the distance over which a force is applied, the less force needed
  • The shorter the distance over which a force is applied, the more force needed

-Machines do not reduce the amount of work!!! The amount of work is always the same whether a machine is used or not.

-There are 6 simple machines that make up all other machines:

Lever - Screw - Inclined Plane - Wheel & Axle - Wedge – Pulley

-Two or more simple machines combined together form Compound Machines

-Almost all machines are compound machines

Energy

-Energy is defined as the ability to do work.

-There are two main types of energy Kinetic & Potential

-Kinetic energy is moving energy and

  • Depends on mass and velocity

-Potential energy is stored energy (also known as energy of position)

  • Depends on mass and height

-Kinetic Energy + Potential Energy = The total energy of a system

  • Examples of Systems: Swing, Pendulum, Roller Coaster

-The Law of Conservation of Energy states that energy cannot be created or destroyed. It can only be transformed or transferred.