Objective 4—Motion, Force, and Energy

Force: a push or a pull; Formula – mass x acceleration = Force

Force is needed to start or stop the motion of an object.  How much force is needed depends on the mass of the object

Balanced Forces: opposing forces are equal; there is no change in the speed or direction of an object

Energy: ability to do work

Potential Energy: energy of position; stored energy

Kinetic Energy: energy of motion

Potential energy of the cannon ball is greatest at letter C

Kinetic energy of the cannon ball is greatest at letter D

 

Energy Form        Description

 

Energy Form    Description

Chemical          stores energy in molecules / bonds

Mechanical       moves objects

Electrical          moves electrons through circuit wires

Sound                vibrates; makes a sound in an ear             

Light                  travels as a wave

Thermal            produces heat; due to motion of atoms

Solar                 provides most of the Earth’s energy; generated by the Sun

Weight: measures the force of gravity on an object; Formula – mass x acceleration due to gravity (9.8 m/s²) = Weight

Velocity: speed in a given direction

Acceleration: rate at which velocity changes

Speed: the rate at which object moves; Formula – distance/time = Speed

 

                        Distance-Time Graph for Table 1

Distance (m)

Time (s)

Work: force acting over a distance; Formula – force x distance = Work

Machine: Tool that makes work easier by changing the size or direction of the force put into it.

Simple Machines:

Inclined Plane: Slanted surface

When the forces are equal neither team is winning and the rope is not moving in either direction.

Unbalanced forces: opposing forces are not equal; can change the speed and direction of an object

The force forward is greater than the force opposing that movement so the car will be moving forward.

Gravity: a force that pulls objects toward one another; gravity varies by location Ex. The gravity on Earth is greater than the gravity on the moon, so a person would weigh more on Earth than on the Moon, but their mass would be the same on both.

Simple Machines Continued:

Wedge: inclined plane that moves

Root tip pushing into the soil

Screw: inclined plane wrapped around a bar

Lever: rigid bar that moves about a fixed point, called the fulcrum

Pulley: rope, chain, or belt wrapped around a grooved wheel

Wheel and Axle: two circular objects of different sizes; the force applied to the wheel is transferred to the axle

Wave: disturbance that transmits energy

Medium: substance (like solid, liquid, or gas) through which a wave travels

Mechanical Wave: waves that require a medium Ex. Ocean waves through water, sound waves through air, seismic waves through the ground

Electromagnetic Waves: waves that do not require a medium; can travel through a vacuum (empty space) Ex. visible light, radio waves, and X-rays can travel through a vacuum or a medium

Amplitude: maximum distance from the resting point

Wavelength: distance between two adjacent crests (peaks) or troughs (valleys)

A is a Crest                                C is a Wavelength

B is a Trough                            D is an Amplitude

Frequency: number of wavelengths in a given time period (Ex. number of wave crests that pass a given point per second)

Mrs. Davis’

8th Grade Science