Chapter 13

Forces of Motion

Velocity n.

• The speed and direction of an objects motion.• The velocity of the train was 30 meters per

second north. • The velocity of the was 50 meters

per second south.

Lesson 1 How can you describe motion?

• is all around you. • Different kinds of motion happen at different

rates. • There are many different types of motion –

. , variable, periodic, , and circular.

http://studyjams.scholastic.com/studyjams/jams/science/forces-and-motion/force-and-motion.htm

Motion

constant vibrational

Speed and Velocity

• Speed is how far an object moves during a certain amount of . Distance/time

• Ex 100m/20s = 5m/s • Motion is always measured in relationship to

some location called a of reference. • Speed and velocity are not the .• Velocity describes the and the

direction of an object’s motion. Ex. North, south, up, or down.

time

point

same

speed

Review

1) What two things do you need to know to find an object’s velocity? 2) Robert moved 28 m in 4 sec. Tallana moved 600 m in 2 min. List these people and their speeds in order from fastest to slowest. 3) Motion is always measured in relationship to some location called a of reference. 4) What is the formula for speed?

Force .

• A push or pull that acts on an object. • The force of the wind was very strong. • Write you own sentence using this starter.

The force of .• Is gravity a force?

Work .

• Done when a force an object.• Work is done only when the object moves at least

partly in the same direction in which the force is applied.

• Work = force x distance• Is work done if I am pushing on the wall? • Is work being done if I am pushing a chair across

the room? • If I am holding on to a ball is work being done?

moves

Power .

• Rate at which work is done.• Since running up the hill is faster than walking,

the amount of power needed to run is greater. • Power = work/time • If I do work faster is there more power

involved?

Lesson 2 What are Forces?• A force is a push or that acts on an object.

• Forces can make a moving object speed up, slow

down, or change . • Forces have both magnitude and direction.

Magnitude measured in Newtons (N) Gravity • Every object in the universe exerts a gravitational

pull on every other object. Only large objects such as are strong enough to be felt.

pull

directions

Earth’s

• An object’s weight is the amount of gravitational force between it and Earth. This force depends on Earth’s size, mass, and how far above Earth the object is.

• Your would be less if you are flying or on another planet, because of less .

weightgravity

Magnetism and Electricity• Magnetism – force that and pulls. • A magnets force is greatest at a magnet’s . • Every magnet has a south and north pole.• North and south poles . If you have a

north and north pole they will repel. • Objects get electrically charged when they gain or

lose electrons. • Electrons often move from one object to another

when the objects are rubbed together.

pushespoles

attract

• Gravity, magnetic, and electric forces as objects get closer together.

• Magnetism and electricity can be by certain objects.

• can’t be blocked. • Electricity and magnetism can push or pull. • Gravity only can .

http://studyjams.scholastic.com/studyjams/jams/science/forces-and-motion/fgravity-and-inertia.htm

increase

blocked

Gravity

pull

Friction

• Friction is the that results when two materials rub against each other.

• Friction slows down objects or keeps them from to move.

• Speed, shape, or affect the amount of friction with other objects.

• Share an example of friction. • Air and water resist motion when a moving

objects tries to go through them.

force

startingtexture

Work and Power

• Work is done when a force an object. • Work is measured in Joules • If the force applied to an object does not move

the object, then work has been done. • Holding an object requires a force, but since the

object does not move, no work is done. • is the rate at which work is done.

When work is done faster power is .

.moves

no

Powerincreased

Review

1) Define force.2) As objects get closer together gravity,

electricity, and magnetism do what? 3) How does friction affect the movement of an

object? 4) When is work done? 5) What is power?

Inertia .

• The tendency of an object to resist any change in motion. Unless a force acts on an object, the object will remain in constant motion.

• Objects with more mass have more inertia than objects with less mass.

• Ex. When a car turns directions your body tends to keep moving in the direction it was moving.

• Inertia - roller coaster. • The seat belt prevents the test dummy’s inertia from

carrying the dummy through the windshield. Think of some other examples.

Lesson 3 What are Newton’s laws of motion?

• Newton’s laws of explain why objects like a ball move the way they do.

• Different forces can act on an object at the time. They may act in different .

• All the forces acting on an object equal the net force.

• The net force will determine whether the object starts moving, , or changes direction.

• Isaac Newton – Newton’s laws, law of gravitation, and used math in studying nature.

motion

directions

stops

Newton’s 1st Law

• Says that unless a net force acts on an object the object will in constant motion. An object at rest stays at rest until a net force acts on it.

• The tendency of an object to any change in motion is inertia.

• Objects with a lot of mass have more than those that don’t have much mass.

• Example When you turn directions in a car or riding a roller coaster. http://www.youtube.com/watch?v=ZFoG7HRF2mE

http://studyjams.scholastic.com/studyjams/jams/science/forces-and-motion/inertia.htm

remain

resist

inertia

Newton’s 2nd Law

• Describes how acceleration, mass, and net force are related.

• Acceleration is the rate at which the of an object changes over time.

• Acceleration = force/mass• The stronger the force acting on an object, the

more that object will . • http://

www.youtube.com/watch?v=iwP4heWDhvw http://studyjams.scholastic.com/studyjams/jams/science/forces-and-motion/acceleration.htm

velocity

accelerate

Newton’s 3rd Law

• When one object exerts a force on a second object, the second object exerts a force on the first object.

• Action- law of motion. Forces are always equal and and always occur in pairs.

• This happens all around us. It is to have one force without an equal and opposite force!

• Ex bumper cars• http://www.youtube.com/watch?v=cxVBbgFJo6Y

http://studyjams.scholastic.com/studyjams/jams/science/forces-and-motion/action-and-reaction.htm

reactionopposite

impossible

Review

1) What is Newton’s first law of motion? 2) Describe Newton’s 2nd law of motion. 3) Explain Newton’s 3rd law of motion. 4) Which of Newton’s laws of motion is

demonstrated by a hammer pounding a nail into a board?

5) What are all the forces acting on an object called?

Machine .

• A device that changes the direction or the amount of force needed to do work.

• Ex. Wheel and axle, pulley, or lever. • They used a machine to help make their work

easier. • Think of an example of when you would want

to use a machine to do work.

Lesson 4 What are simple machines?

• Remember work is done when a force causes an object to .

• A machine changes the direction or amount of force needed to do work.

• Simple machines are machines with parts. • Ex. Wheel and axle, pulley, inclined plane, and

lever. • Machines don’t reduce the amount of work that

needs to be done they just make it .

move

few

easier

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Pulley

• Consists of a rope or cable that runs through a grooved wheel.

• and drapery rods use pulleys. • A block and tackle is a system of pulleys that

make it easier to lift very heavy objects.

Flagpoles

Wheel and Axle

• Made up of a circular object such as a doorknob, and a shaft.

• They the amount of force needed to do work.

• Steering wheel of a car and pulling a bucket out of a well with a crank are some examples.

reduce

Lever

• Where a bar rotates around a fixed point called a . .

• Levers do work using the bar, fulcrum, a load, and a you apply.

• As the position of the fulcrum changes the amount of force needed to move the box will change.

• The farther the fulcrum is from the person using the lever, the the lever is to use.

• Ex. Wheel barrow, pliers, clothespins.

fulcrum

force

easier

Inclined planes

• A is an example of an inclined plane.

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

• Can be big or small. • Other inclined planes include screws (inclined

plane is wrapped around it) and doorstops.

ramp

Complex Machines

• A machine that uses or more simple machines.

• Many complex machines use , gravity, burning fuel, human force, or magnetism.

• Example Go carts, sailing ships. • What would be some other examples of

complex machines?

two

electricity

Review

1) What are two examples of a wheel and axle that can make work easier?

2) What are all of the parts of a lever? 3) What is a complex machine? 4) What simple machine are you using when

you raise or lower a flag on a flagpole?