Chapter 1 “Matter in Motion” Sections 1-4 Pages 4-59

Reference Point• Observe motion by using

a reference point • Reference Point: An

object that appears to stay in place(use non moving objects- such as trees or buildings)

• Motion: An object's change in position relative to a reference point

I feel the need…the need for Speed• Speed: the distance traveled by

an object divided by the time taken to travel that distanceSI Units: m/s, km/h, ft/s, mi/h

• Determining average speed: Average speed= total distance/total

timeExample: A person swims 105 m in

70 s.Average speed = 105 m/70 sAnswer= 1.5 m/sTry on your own: page 6/Math Focus

Velocity: Direction Matters

• Velocity: the speed of an object in a particular direction

• Different from speed because it includes direction!

• Two ways to change velocity: 1. changing speed or 2. changing direction

Finding Resultant Velocity• When you combine two

velocities that are in the same direction, add them together to find the resultant velocity.

• When you combine two velocities that are in opposite directions, subtract the smaller velocity from the larger velocity to find the resultant velocity. The resultant velocity is in the direction of the larger velocity.

Acceleration• Acceleration: the rate at

which velocity changes over time

• An object accelerates if its speed, direction, or both changes

• Positive acceleration (increase in velocity)

• Negative acceleration or deceleration (decrease in velocity)

Calculating Average Acceleration• Average acceleration= final velocity-starting velocity

time it takes to change velocityExample: page 8 5 m/s – 1 m/s = 1 m/s² south 4 s• You can use graphs to show acceleration using time

Circular Motion

• Centripetal acceleration: acceleration that occurs in a circular motion

• Examples- You on Earth, Moon orbiting Earth, You on a Ferris Wheel, Windmill blades

May the Force Be with You

• Force: A push or pull exerted on an object in order to change the motion of the object; force has size and direction

• Force is expressed in the unit called the newton (N).

Forces Acting on Objects

• All forces act on objects. • Just because a force

acts on an object doesn’t mean that object will change motion.

• There are unseen forces known as gravity. It is what keep air around you and on Earth.

Determining Net Force• Net Force: the combination

of all the forces acting on an object. Depends on direction of forces.

• If all of the forces act in the same direction you must add forces to determine the net force.

• If the forces are different/opposite directions you will need to subtract.

Balanced and Unbalanced Forces • Balanced Forces: The force

that does not cause change in the motion of a moving object. It also does not cause a nonmoving object to start moving.

• Unbalanced Forces: The force that produces a change in motion, such as a change in speed or change in direction. These forces are necessary to cause nonmoving objects to start moving.

The Source of Friction

• The amount of friction between surfaces depends on many factors. The two factors include:

1. The force pushing surfaces together

2. The roughness of the surface

The Effect of Force on Friction • The amount of friction

depends on the force pushing the surfaces together.

• Close contact increases friction

• Objects that weigh less exert less downward force than heaver objects

• Changing the amount of surface comes in contact does not change the amount of friction

The Effect of Rougher Surfaces on Friction

• Friction is greater between rough surfaces have more microscopic hills and valleys

• Friction is caused by chemical bonds that are formed and broken between the hills and valleys of two surfaces NOT the climb. This is called “stick and slip.”

Types of Friction• Kinetic Friction: friction

between two moving surfaces (LARGE-moving/pushing a heavy object on the floor OR SMALL-using wheels under the object to push/move the object)

• Static Friction: when a force is applied to an object and it does not cause any movement

Friction: Harmful and Helpful

• Helpful: brakes on car• Harmful: erosion on

land• Reduce Friction- use

lubricants such as oil, grease and wax

• Increase Friction- using textured substances (like sand, salt, etc.)

The Effects of Gravity on Matter

• All matter has mass, gravity is a result of mass.

• The size of the Earth (mass) is so large that you must exert a force to overcome the gravitational force between the object and Earth

Newton and the study of Gravity

• Why do objects fall toward Earth?

• What keeps the planets moving in the sky?

Newton realized these were two parts of the same question not two different questions.

Law of Universal Gravitation

• Newton’s law describes the relationship between gravitational force, mass and distance.

• This law is called universal because it applies to all objects in the universe.

Law of Universal Gravitation

• Part 1: Gravitational Force

increases as mass increase.

• Part 2:Gravitational Force

decreases as distance increases.

Weight as a Measure of Gravitational Force

• Mass is constant in the universe.

• Weight varies by gravity.• The weight of an object is a

measure of the gravitational force on an object.

• Use a Spring Scale to measure weight.

• Mass is measured in grams.• Weight is measured in

Newtons. • 100 grams = 1 Newton