Matter in Motion

Chapter 1

Page 3

Measuring motion

Section 1

Measuring Motion

• An objects change in position over time when compared with a reference point

Motion is relative

• If you are in a car that is going at the same speed, the other car will not by moving with respect to you. But both cars are moving with respect to the ground.

Reference point

• Any object that will appear to stay in place

• Moving objects can be used as reference points

Point of Reference cont

• In talking about motion, it is important to indicate your point of reference. In the case of moving automobiles, it is usually assumed the speed is with respect to the ground. But there are situations where the speed or velocity may be with respect to another object or an observer.

Example

• For example, suppose a car was traveling at 60 miles per hour (mph) and hit another car, but there was hardly a dent. The reason is that the second car was traveling in the same direction at 59 mph, so the car was going only 1 mph with respect to the second car when it hit it.

Sun looks like it is moving in the sky

• The sun appears to move across the sky, when the earth is actually spinning and causing that apparent motion.

• Usually, we consider motion with respect to the ground or the Earth. Within the Universe there is no real fixed point.

• The basis for Einstein's Theory of Relativity is that all motion is relative to what you define as a fixed point.

Speed Depends on distance and time

• Speed the rate at which an object moves

• SI unit is meters/seconds (m/s)

Average Speed

• Objects do not travel at constant speed therefore we calculate average speed

• Average Speed = Total Distance

Total time

Calculating Average Speed

Answers

Practice

Find the average

Practice

Steps

Practice

Answers

Velocity

• The speed of objects in a particular direction

Velocity

• The final component in explaining an object's velocity is including a relative direction. For example, a car that travels 100 meters in 10 seconds, in the westerly

direction, would have a velocity of 10 m/s west.

Acceleration: The rate at which velocity changes

• measured by taking the change in velocity of an object divided by the time is took to change that velocity:

Acceleration

• For example, if an object speeds up from a velocity of 240 meters/second to 560 meters/second in a time period of 10 seconds, the acceleration is (560 - 240)/10 = 320/10 = 32 m/s/s or 32 m/s².

Practice Problems Math Break

• Page 5

• Page 9

Graphing

The Speed a Car travels

Speed

0

100

200

300

400

500

1 2 3 4 5

Time (h)

Dis

tan

ce (

km)

What is Force

Section 2

Terms to learn: force, net force, newton

Force

• Push or pull

http://adventure.howstuffworks.com/extreme-sports-pictures.htm

Determining the Net Force

• Net force: The sum of all the forces which act upon an object

Vectors

Unbalanced = Motion

Balanced = No Motion

Friction

Section 3

Friction

• Any force that opposes motion b/t two surfaces that are touching

Sliding Friction

• Very effective a opposing force

• Lot of force must be exert to overcome

Rolling Friction

• A rolling wheel requires a certain amount of friction so that the point of contact of the wheel with the surface will not slip.

Fluid Friction

• Friction forces formed b/t liquids and another surface

• Streamlining reduces fluid friction

Static Friction

• The force of friction that is equal to force applied

Friction = Force Applied= No Motion

Ways to change Friction

• Reduce– Lubrication– Streamlining

• Increase– Add texture– Add force

Gravity: A force of Attraction

Section 4

Gravity

• A force of attraction b/t object due to its mass

Newton’s Idea

• Unbalanced forces caused an apple to fall from a tree

• He realized the two forces are one gravity

Law of Universal Gravitation

• All objects in in the universe attract each other through gravitational force

Forces in action

• Mass– How much matter it

contains. – It is measured in

grams (g) or kilograms (kg) but is NOT a force.

• Weight– The force caused by

gravity pulling down on the mass of an object.

– It is measured in Newtons (N).

Size of Force Depends

• Mass– Larger the mass the

greater the force of gravity

• Distance– Closer the distance

the greater the force of gravity