# 7th Grade Science Notes Chapter 4 ```7th Grade Science - Chapter 4 Notes
Force - any push or pull on an object
Forces have size and direction. Arrows show size by their length and direction by which way they
point.
Forces can affect objects by changing their speed and direction.
Noncontact Force - a force that pushes or pulls an object without touching it. Ex: gravity, electricity,
magnetism
Contact Force - is a push or pull applied by one object to another object that is touching it. Also
called mechanical forces.
Friction - is a contact force that resists the sliding motion between two objects that are touching
Gravity - is a noncontact attractive force that exists between all objects that have mass.
The closer two objects are, the stronger the gravitational force between them and vice versa.
The greater the mass of two objects, the stronger the gravitational force between them and vice
versa.
Net Force - the sum of the forces acting on an object.
Balanced Forces - when the net force on an object is 0 N, caused by the forces acting on it.
Unbalanced Forces - when the net force on an object is not 0 N, caused by the forces acting on it.
Unbalanced forces cause object to change their motion.
***Know how to calculate net force***
Energy - the ability to cause a change
Kinetic Energy - the energy an object has because it is in motion. The faster or bigger an object is
when moving, the more kinetic energy is has and vice versa.
Electric Energy - the energy that an electric current carries
Potential Energy - stored energy that depends on the interaction of objects, particles, or atoms
Gravitational Potential Energy - a type of potential energy stored in an object due to its height
above the Earth’s surface.
Chemical Energy - is energy that is stored in and released from bonds between atoms
Nuclear Energy - energy stored in and released from the nucleus of an atom. Nuclear fission releases
energy by ‘splitting’ the nucleus of an atom.
Mechanical Energy - the sum of potential energy and kinetic energy in a system of objects
Thermal Energy - is the sum of the kinetic energy and potential energy of the particles that make up
an object
Sound Energy - is energy carried by sound waves
Seismic Energy - is the energy transferred by waves moving through the ground
Radiant Energy - the energy carried by electromagnetic waves
Energy Transformation - is the conversion of one form of energy to another
The Law of Conservation of Energy - says that energy can be transformed from one form to
another, but it cannot be created or destroyed
Work - is the transfer of energy that occurs when a force makes an object move in one direction of
the force while the force acts on the object.
Work Equation - Work = force x distance
or
W = Fd
Force is expressed in Newtons, distance is in meters. The product is the newton-meter or joule.
Heat - when thermal energy moves from a region of higher temperature to one of lower temperature.
Simple Machines - are machines that do work using one movement. All simple machines make work
easier by either changing the direction or size of the force.
Inclined Plane - is a flat, sloped surface (ramp)
Wedge - is an inclined plane that moves
Screw - is an inclined plane wrapped around a cylinder
Level - a simple machine that pivots around a fixed point
Wheel and Axle - a shaft attached to a wheel of a larger diameter so both rotate together
Pulley - a grooved wheel with a rope or cable wrapped around it. Two types: fixed &amp; moveable.
Complex Machine - two or more simple machines working together
Efficiency - is the ratio of output work to input work
Efficiency = output work/input work x 100%
```