Table of Contents The Nature of Force Friction and Gravity Newton’s First and Second Laws Newton’s Third Law Rockets and Satellites

What is a FORCE? - The Nature of Force a push or a pull vector because they have magnitude (# indicating strength) and a direction 6N 50 N What are some examples of forces?

Named for Sir Isaac Newton Very light, small amt. What is a Newton? SI unit of force Abbreviated N Named for Sir Isaac Newton Very light, small amt. Replaces “pound” in our system = 1kgm/s2 Measured with a spring scale

- The Nature of Force Combining Forces-The combination of all forces acting on an object is called the net force.

Balanced Forces - The Nature of Force Balanced forces acting on an object do not change the object’s motion.

Unbalanced Forces - The Nature of Force Unbalanced forces acting on an object result in a net force and cause a change in the object’s motion.

Balanced and Unbalanced Forces - The Nature of Force Balanced and Unbalanced Forces Use the link to the physics classroom to see how vectors interact. http://www.physicsclassroom.com/Physics-Interactives/Vectors-and-Projectiles/Vector-Addition/Vector-Addition-Interactive

- Newton’s FIRST Law Law of Inertia

Force = mass X acceleration - - Newton’s Second Law WRITE DOWN YOUR NEWTON WT. Force = mass X acceleration A speedboat pulls a 55-kg water-skier. The force causes the skier to accelerate at 2.0 m/s2. Calculate the net force that causes this acceleration. Read and Understand What information have you been given? Mass of the water-skier (m) = 55 kg Acceleration of the water-skier (a) = 2.0 m/s2

Calculating Force - Newton’s Second Law A speedboat pulls a 55-kg water-skier. The force causes the skier to accelerate at 2.0 m/s2. Calculate the net force that causes this acceleration. Plan and Solve What quantity are you trying to calculate? The net force (Fnet) = __ What formula contains the given quantities and the unknown quantity? a = Fnet/m or Fnet = m X a Perform the calculation. Fnet = m X a = 55 kg X 2.0 m/s2 F = 110 kg • m/s2 F = 110 N

Calculating Force - Newton’s Second Law A speedboat pulls a 55-kg water-skier. The force causes the skier to accelerate at 2.0 m/s2. Calculate the net force that causes this acceleration. Look Back and Check Does your answer make sense? A net force of 110 N is required to accelerate the water-skier. This may not seem like enough force, but it does not include the force of the speedboat's pull that overcomes friction.

Calculating Force Practice Problem - Newton’s Second Law What is the net force on a 1,000-kg object accelerating at 3 m/s2? 3,000 N (1,000 kg X 3 m/s2)

Calculating Force Practice Problem - Newton’s Second Law What mass can be accelerated at 14 m/s2 by 350 N? m= F/a m= 350 N/14 m/s2 M = 25 kg

Newton’s First and Second Laws Outlining As you read, make an outline about Newton’s first and second laws. Use the red headings for the main topics and the blue headings for the subtopics. Newton’s First and Second Laws Newton’s First Law of Motion Inertia Inertia Depends on Mass The Second Law of Motion Changes in Force and Mass

End of Section: Newton’s First and Second Laws

- Newton’s Third Law Newton’s 3rd Law

Calculating Momentum - Newton’s Third Law Which has more momentum: a 3.0-kg sledgehammer swung at 1.5 m/s or a 4.0-kg sledgehammer swung at 0.9 m/s? Read and Understand What information have you been given? Mass of smaller sledgehammer = 3.0 kg Velocity of smaller sledgehammer = 1.5 m/s Mass of larger sledgehammer = 4.0 kg Velocity of larger sledgehammer = 0.9 m/s

Calculating Momentum - Newton’s Third Law Which has more momentum: a 3.0-kg sledgehammer swung at 1.5 m/s or a 4.0-kg sledgehammer swung at 0.9 m/s? Plan and Solve What quantities are you trying to calculate? The momentum of each sledgehammer = __ What formula contains the given quantities and the unknown quantity? Momentum = Mass X Velocity Perform the calculation. Smaller sledgehammer = 3.0 km X 1.5 m/s = 4.5 kg•m/s Smaller sledgehammer = 4.0 km X 0.9 m/s = 3.6 kg•m/s

Calculating Momentum - Newton’s Third Law Which has more momentum: a 3.0-kg sledgehammer swung at 1.5 m/s or a 4.0-kg sledgehammer swung at 0.9 m/s? Look Back and Check Does your answer make sense? The 3.0-kg hammer has more momentum than the 4.0-kg one. This answer makes sense because the 3.0-kg hammer is swung at a greater velocity.

Calculating Momentum Practice Problem - Newton’s Third Law A golf ball travels at 16 m/s, while a baseball moves at 7 m/s. The mass of the golf ball is 0.045 kg and the mass of the baseball is 0.14 kg. Which has the greater momentum? Golf ball: 0.045 kg X 16 m/s = 0.72 kg•m/s Baseball: 0.14 kg X 7 m/s = 0.98 kg•m/s The baseball has greater momentum.

Calculating Momentum Practice Problem - Newton’s Third Law What is the momentum of a bird with a mass of 0.018 kg flying at 15 m/s? 0.27 kg•m/s (0.018 kg X 15 m/s = 0.27 kg•m/s)

Conservation of Momentum - - Newton’s Third Law Conservation of Momentum In the absence of friction, momentum is conserved when two train cars collide.

Conservation of Momentum - Newton’s Third Law Previewing Visuals Before you read, preview Figure 18. Then write two questions that you have about the diagram in a graphic organizer like the one below. As you read, answer your questions. Conservation of Momentum Q. What happens when two moving objects collide? A. In the absence of friction, the total momentum is the same before and after the collision. Q. What is the momentum of an object? A. Its mass multiplied by its velocity

What Is a Satellite? - Rockets and Satellites A projectile follows a curved path because the horizontal and vertical motions combine.

What Is a Satellite? - Rockets and Satellites The faster a projectile is thrown, the father it travels before it hits the ground. A projectile with enough velocity moves in a circular orbit.

What Is a Satellite? - Rockets and Satellites Depending on their uses, artificial satellites orbit at different heights.

Identifying Main Ideas - Rockets and Satellites Identifying Main Ideas As you read the section “What Is a Satellite?” write the main idea in a graphic organizer like the one below. Then write three supporting details that further explain the main idea. Main Idea A satellite stays in orbit due to… Detail Detail Detail its inertia Earth’s gravity Earth’s shape

End of Section: Rockets and Satellites

Graphic Organizer Type of Friction Occurs When Example Static Sliding Friction between an unmoving book and desk An object is not moving Static Two solid surfaces slide over each other Sliding Rubber pads on a bicycle’s brakes Rolling An object rolls across a surface Ball bearings in skateboard wheels A solid object moves through a fluid Fluid Air resistance

End of Section: Graphic Organizer

Gravity - Friction and Gravity Two factors affect the gravitational attraction between objects: mass and distance. Direct relationship Indirect relationship

Gravity What has a greater affect on gravitational force: an equal change of mass or distance? (Use the info to the right to help!)

Gravity - Friction and Gravity The force of gravity on a person or object at the surface of a planet is known as weight.

Friction What is it? Compare the time of a toy car on a smooth track to one on a bumpy track (with sandpaper). Take 3 trials for each type of track and average them.

Friction What is it? What 2 factors does it depend on? 1. 2. Heat is a by-product of friction. What types of friction are there? And how do they differ? 3. 4.

Free Fall - Friction and Gravity Use the graph to answer the following questions.

Free Fall - Friction and Gravity Interpreting Graphs: What variable is on the horizontal axis? The vertical axis? Time is on the horizontal axis, and speed is on the vertical axis.

Free Fall - Friction and Gravity Calculating: Calculate the slope of the graph. What does the slope tell you about the object’s motion? The slope is 9.8. The speed increases by 9.8 m/s each second.

Free Fall - Friction and Gravity Predicting: What will the speed of the object be at 6 seconds? 58.8 m/s

Free Fall - Friction and Gravity Drawing Conclusions: Suppose another object of the same size but with a greater mass was dropped instead. How would the speed values change? The speed values would not change.

Air Resistance - Friction and Gravity Falling objects with a greater surface area experience more air resistance.

Comparing and Contrasting - Friction and Gravity Comparing and Contrasting As you read, compare and contrast friction and gravity by completing a table like the one below. Friction Gravity Pulls objects toward one another Effect on motion Opposes motion Types of surfaces involved, how hard the surfaces push together Depends on Mass and distance Measured in Newtons Newtons