chapter 13 – forces in motion

Chapter 13 – Forces in

Motion

Types of MotionConstant Motion – motion that is constant and steady

Types of MotionVariable Motion – motion that moves in many directions and at many speeds

Types of MotionPeriodic Motion – back and forth steady movement

Types of MotionCircular Motion – movement in circles

Types of MotionVibrational Motion – movement that is quick, back and forth vibrations

Speed• The distance an object travels

in a certain amount of time.• To find the speed divide the

distance and the time it took to go that distance

• S = D/T• Sammy the Snail

VelocityDescribes the speed and direction of an object’s motion.Example: The plane is moving west at 300mph.

Speed and Velocity

Point of ReferenceMotion measured as a relationship between two objects.

Referencepoint

Force• A push or a pull that acts

on an object.• Forces can make a moving

object speed up, slow down, or change directions.

Gravity• The force of attraction

between two objects causing them to have weight.

• Examples• Apple falling out of a tree.• Skydiver landing on the

ground.

Magnetism• A force that pushes and

pulls on other objects• Push – two north poles will

push away from each other• Pull – a north pole and a

south pole will pull toward each other

Electricity• All objects that are

electrically charged will exert forces on each other.

• Oppositely charged objects are attracted to each other.

• Objects with the same chare are repelled, and move away from each other

Friction• The force between moving parts that tends to

slow them down.

Magic School Bus – Plays Ball

Work• Work is done when a force moves an object.• If the force does not make the object move,

then no work has been done• Work is done only when the object moves

Scientific Definition

Formula

Work(Joules)

Energy used when a force moves an object

Work = force x distance

Power• The rate at which work is done.• Walking up a hill and running up the same hill

take the same amount of work. Since running up the hill is faster than walking, the amount of power needed to run is greater.

Scientific Definition

Formula

Power(Watts)

Rate at which work is done

Power = work/time

Newton’s Laws of Motion

The Science of Sports

Newton’s 1st Law of Motion• An object at rest stays at rest until a force

acts on it. An object moving at a constant speed will continue to move in a straight line and at a constant speed until a force acts on it.

Inertia• The tendency of an object

to resist any change in motion

• The physical property that keeps an object moving after the accelerating force is gone.

Newton’s 2nd Law of Motion• Acceleration is produced when a force acts

on a mass. The greater the mass (of the object being accelerated) the greater the amount of force needed (to accelerate the object).

Acceleration• The rate at which the

velocity of an object changes over time.

Newton’s 3rd Law of Motion• For every action there is an equal and

opposite re-action.

Air Resistance• The force that acts to slow

down any object moving through air.

Pulley• A pulley consists of a rope or

cable that runs through a grooved wheel.

• Makes work easier by changing the direction of the force

• Examples – flagpole, window blinds

Wheel and Axle• A wheel and axle is made

up of a circular object and a shaft.

• Examples – doorknob, bicycle wheel

Lever• A lever is a stiff bar rotating

around a fixed point called a fulcrum.

• Makes work easier by changing the direction of a force.

• Examples – hammer, shovel

Inclined Plane• An inclined plane consists

of a flat surface with one end higher than the other.

• Examples – wheelchair ramp, playground slide

Screw• An incline planed wrapped

around a center rod• Examples – base of jar lid,

light bulb base

Wedge• A wedge is two inclined

planes placed back to back• Examples – knife, axe, fork,

nail, doorstop