MATTER IN MOTION

Vocabulary Motion: an objects change in position relative to a reference point Speed: the distance traveled divided by the time interval during which the motion occurred.

Speed practice Units for measuring speed: m/s, mph, km/s Finding your average speed Average speed = total distance/total time Example: If I traveled in my car for 4 hours and a distance of 360 kilometers, what was my average speed? Let’s practice! What will we need to find the average speed a human walks?

Average Human’s Walking Speed StudentsTrial 1Trial 2Trial 3Average ft/sec A B C What is the average of all three walkers? ___________________

Vocabulary Continued Velocity: the speed of an object in a particular direction Example: A car was driving 35 mph, North. Resulting velocity: Combining more than one velocity. Example: a person walking backwards in a bus which is traveling forward. The man is walking at 1 m/s backwards and the bus is traveling 15 m/s forward, so the man’s resulting velocity is: ______________________

Acceleration Acceleration: the rate at which velocity changes over time; an object accelerates if its speed, direction, or both change Positive acceleration: an increase in velocity Negative acceleration: a decrease in velocity

Finding Acceleration Average acceleration = Final velocity – starting velocity time it takes to change velocity Example: What is the average acceleration of a subway train that speeds up from 9.6 m/s to 12 m/s in 0.8 s on a straight track? 3 m/s/s

WHAT IS FORCE?

Vocabulary Force: a push or a pull exerted on an object in order to change the motion of the object; force has a size and direction. Newton (N): The SI Unit for force Net Force: The combination of all of the forces acting on an object

Understanding Net Force

More on Net Forces

Unseen Forces What are some unseen forces? Magnets Gravity Static Electricity

Balanced and Unbalanced Forces Balanced Force: When the forces on an object produce a net force of 0 N. Unbalanced Force: When the net force on an object is not 0 N. It produces a change in motion

Friction and it’s affects Friction Defined: A force that opposes motion between two surfaces that are in contact. Gently rub your hands together rapidly The harder you push the object increases the amount of friction between the objects, which increases the heat The rougher the surface the more “hills and valleys” it has, also increases friction

Types of Friction Kinetic Friction The word “kinetic” means moving. So, kinetic friction is the friction between moving surfaces Static Friction The word “static” means not moving. So, when force is applied to an object, (you try pushing on a heavy dresser) and it does not move, that is static friction.

Usefulness of friction What are some good uses of friction? Brake pads on a car Rubbing sticks together to create a fire How can Friction be a bad thing? Car engines can over-heat, due to friction Solution: Lubrications, like engine oil Getting holes in your socks Solution: buy better socks…

Gravity Gravity defined: A force of attraction between objects that is due to their masses ALL matter has mass. Gravity is a result of mass. Therefore, all objects in the universe have gravity. Which means all objects experience an attraction to all other objects. The larger the mass of an object the more pull of gravity it has The Earth is the largest object to us, therefore we are pulled to it more than any other object. Sir Isaac Newton “discovered” gravity and the Law of Universal Gravitation was created in 1622 It is universal, because it is true everywhere in the universe!

Imagine if… Tear out a separate sheet of paper and write this prompt at the top of the page: Imagine if the Law of Universal Gravitation no longer existed… How would this change things? What would we need to do to change how we live? Think about how we would need to get food and water. Think about how our habitats would change. Etc.

Gravity and Motion Objects fall to the ground at the same rate, because the acceleration is due to gravity is the same for all objects Remember: Acceleration is the rate at which velocity changes.

Finding the Velocity of a Falling Object v = g X t To find the change in velocity you need to understand that g= the acceleration due to gravity on Earth, or 9.8 m/s/s The “t” is how many seconds the object is falling.

Practice finding the Velocity of a Falling Object If an object falls for 3 seconds, what is its velocity? 29.4 m/s What if an object falls for 10 seconds, what is its velocity? 98 m/s

Exceptions to the rule… Finding the velocity of an object on Earth would be easy, if we lived in a vacuum. However, because we have wind resistance – friction, objects don’t continually speed up, this is called: Terminal Velocity: the constant velocity of a falling object when the force of air resistance is equal in magnitude and opposite in direction to the force of gravity. Basically you are still falling, but you are no longer speeding up.

Free Fall: the motion of a body when only the force of gravity is acting on the body. If we lived in a vacuum we would not have wind resistance and would continually speed up until we hit the ground. This means hail would travel at 11.2 km/s, or 25,000 mph A bullet travels at 1,700 mph When objects orbit larger objects, such as the International Space Station orbiting the Earth, they are in Free Fall When objects are orbiting, they are continually falling, but they just keep missing.

Projectile Motion Defined: the curved path that an object follows when thrown, launched, or otherwise projected near the surface of Earth.

Physics Math Practice… Resulting Velocity = combination of more than one velocity Unit: m/s and the direction the object is traveling. Average acceleration = Final velocity – starting velocity time it takes to change velocity Unit: m/s/s Average speed = total distance/total time Unit: m/s, mph, km/h Net Force = if the two are going in the same direction it is an addition problem, opposite direction it is a subtraction problem Unit: N and the direction the object is traveling v = g X t Unit: m/s

Math Practice Find the resulting velocity if you are on a bus traveling north at 12 m/s, you stand up and walk backwards at 3 m/s. What is your resulting velocity? 9 m/s north Find the Net force of an object, if one person is pull a box to the right with 45 N of force. There is a second person pulling the box in the other direction 23 N, What is the Net Force? 22 N Right Find the average acceleration of a car the started out traveling 15 m/s and ended up going 25 m/s, in a straight line, and took them 5 seconds. 2 m/s/s

More Math!!!! Find the average speed a truck traveled if they were on the road for 6 hours and traveled 240 miles. 40 mph Find the change in velocity of an object that fell to Earth for 13 seconds, if it were in a vacuum m/s Bonus Question: Solve the same problem if the object were dropped on Venus… The rate of acceleration on Venus is: 9.5 m/s/s. Also, solve for Jupiter, with its acceleration being: 24.5 m/s/s. And finally the Sun, at: 275m/s/s Venus: m/s Jupiter: m/s Sun: 3,575 m/s

Newton’s Laws of Motion