Motion

Edited from CSCOPE by John Vose, Sixth Grade Science Teacher, Copperas Cove Junior High School, Copperas Cove, Texas

What is motion anyway?

Motion is a change in position, measured by distance and time.

Speed

We talk about speed everyday. Speed is the distance traveled by a

moving object per unit of time. Speed affect the energy of an

object. The faster it moves, the more kinetic energy it has.

Speed = distance time

Velocity

Velocity and Speed are like fraternal twins- very similar, but with important differences.

Velocity is speed in a given direction. 35 mph NORTH 4 km/sec EAST

Which is which?

100 m/s right 1500 km/s 65 m/s north 3000 km/s

VelocitySpeedVelocitySpeed

What changes motion?

Force!! F = mass x acceleration A force is a push or pull that can

change motion A force can move an object, OR A force can transfer energy to an

object without moving it For example, pushing on a wall doesn’t

move the wall, but energy is being transferred.

Unbalanced Forces

In order for an object to move, there must be unbalanced forces.

Like tug of war…the winners are pulling the other team with more force; therefore the pulling forces are unbalanced.

How can force affect motion?

Resistance forces (friction or wind) that oppose motion can slow down motion.

A force in the same direction can speed up motion.

A force from the side can change the direction of motion (this is also acceleration)

Kinetic Energy – Energy of Motion

Speed and mass affect the kinetic energy of an object.

If two objects are moving at the same speed, but one object has a greater mass, then the object with the greater mass will have more kinetic energy.

The more mass in an object, the more force needed to move it.

Acceleration

Acceleration is the rate of change in velocity.

Acceleration = Change in velocity (m/s)

Time (s) Example: 0 to 60mph in 3s

Friction

Friction is a force that opposes motion.

Can be caused by wind, water, surface texture, etc.

Resistance Force

Have you ever ridden down the street on your bike and felt the wind push against you?

That’s air resistance! Air resistance is the frictional force

from the air that resists forward motion

Momentum

Momentum is the property that a moving object has because of its mass and velocity.

All moving objects have momentum.

Momentum = mass x velocity

Sir Isaac Newton

Isaac is famous for his discovery of gravity. He is also known for his three laws that explain all aspects of motion.

Newton’s First Law

An object at rest will remain at rest, and a moving object will remain at a constant velocity unless unbalanced forces act on it.

** Inertia- is the term used to describe the tendency of an object to remain in motion or stay at rest.

Newton’s Second Law

Motion produced by unbalanced forces.

The units of force are “Newtons”

1 N = 1 kg x m/s s1N is the force on a 1kg mass that will

accelerate that mass at 1 m/s2.

Newton’s Third Law

For every action, there is an equal and opposite reaction.