Chapter 2 - Forces 2.1 The Nature of Force

I. Essential Question: What are forces and how do they affect motion?

II. Key Vocabulary Force: a push or a pull Newton: the unit used to measure the strength of a force. Net force: the combination of all of the forces on an object Balanced force: when the net force is zero; results in no motion. Unbalanced force: a nonzero net force; results in motion.

III. Key Concepts Force is a vector that is defined by its strength and its direction. It is measured in newtons (N). If forces push in the same direction, add them together to find the net force. If forces push in opposite ways, find the difference between them to find the net force.

III. Key Concepts If the net force is 0 N, then the force is balanced and there it no motion caused. If the net force is anything other than 0 N, then the force is unbalanced and there is motion.

Chapter 2 - Forces 2.2 Friction

I. Essential Question: What factors affect friction?

II. Key Vocabulary Friction: the force that two surfaces exert on each other when they rub against each other. Sliding friction: when two solid surfaces slide over each other. Static friction: acts between objects that aren’t moving.

II. Key Vocabulary Fluid friction: when a solid object moves through a fluid. Rolling friction: when an object rolls across a surface.

III. Key Concepts Friction is affected by the types of surfaces and the strength of the forces on the surfaces. Smooth surfaces have less friction. Friction increases with greater force.

III. Key Concepts Friction pushes in the opposite direction of motion. Rolling friction is easier to overcome than sliding friction.

IV. Exploration Experimenting with Friction Lab

Chapter 2 - Forces 2.2 Gravity

I. Essential Question: What factors affect gravity?

II. Key Vocabulary Gravity: a force that pulls objects toward each other. Mass: the measure of the amount of matter in an object, measured in kilograms (kg). Weight: a measure of the force of gravity on an object; measured in newtons (N).

III. Key Concepts Gravity acts everywhere in the universe. The law of universal gravitation states that all objects with mass are attracted to one another. Gravity depends on mass and distance. More mass = more gravity. More distance = less gravity

III. Key Concepts Mass never changes, but weight does depending on gravity. Gravity = about 1/6 on the Moon Gravity = about 1/3 on Mars

IV. Exploration Question: How does the amount of gravity a planet has affect the distance a person could jump when compared to the distance they could jump on Earth?

IV. Exploration Background Info: How does the amount of gravity a planet has affect a person’s weight on that planet?   Would a person weigh more on Earth or Jupiter? Why?

IV. Exploration Hypothesis: If you were to jump forward on that planet, would the distance of your jump be longer or shorter than the distance of your jump on Earth? Why? If…then…because…

IV. Exploration Procedure: Stand behind the line that is taped on the floor. Jump forward, as far as you can. Stay standing on the spot where you landed after your jump. After you’ve jumped, your partner should measure the distance you traveled in your jump with a meter stick. Round to the nearest centimeter. Now, reverse roles so that your partner is the one jumping, and you are the one measuring the distance of his or her jump. Reminder: You are NOT running before you jump. Just jump straight forward from the taped line on the floor.

DISTANCE OF JUMPS ON DIFFERENT PLANETS IV. Exploration Distance of your Jump on Earth: ________________ cm DISTANCE OF JUMPS ON DIFFERENT PLANETS Location Distance on Earth ÷ Gravity = Distance on Other Planet Mercury   0.4 Venus 0.9 Mars Jupiter 2.9 Saturn 1.3 Uranus Neptune 1.2 Earth’s Moon 0.2

V. Understanding and Applying What happened when you divided by a number less than 1? Compared to Earth, were these planets larger or smaller? On which planet/celestial body could you jump the farthest? Why? Which planet had the greatest gravitational pull? Does that make sense with what you already know about gravity? Why or why not?

2.3 Newton’s Laws of Motion Chapter 2 - Forces 2.3 Newton’s Laws of Motion

I. Essential Question: What are Newton’s Three Laws of Motion?

II. Key Vocabulary Inertia: an object’s resistance to change in motion.

III. Key Concepts The First Law of Motion: An object at rest will stay at rest, and an object in motion will stay in motion, unless acted upon by a nonzero net force. Called the law of inertia. Objects with more mass have more inertia and are harder to move.

III. Key Concepts The Second Law of Motion: An object’s acceleration depends on its mass an on the net force acting on it. Force = mass times acceleration; F = m x a If you increase the force and keep the mass the same, the acceleration will increase. If you reduce the mass of an object but keep the force the same, acceleration will also increase.

III. Key Concepts The Third Law of Motion: If one object exerts a force on another object, then the second object exerts a force of equal strength in the opposite direction on the first object. For every action there is an equal and opposite reaction. The first force is the “action” and the second force is the “reaction”. These actions do not cancel each other out because they act on different objects. See page 279 for examples.

IV. Exploration

V. Understanding and Applying

Chapter 2 - Forces 2.4 Momentum

I. Essential Question: What is an object’s momentum?

II. Key Vocabulary Momentum: a characteristic of a moving object that is related to the mass and the velocity of the object. Law of conservation of momentum: in the absence of outside forces, the total momentum of objects that interact does not change.

III. Key Concepts To find momentum, multiply the object’s mass by its velocity. The unit for momentum is (kg)(m/s). The more momentum an object has, the harder it is to stop the object. Greater mass = greater momentum Greater velocity = greater momentum

III. Key Concepts When two objects collide and do not stick together, the object going faster will slow down and the object going slower will speed up. When two objects collide and stick together, the two objects share the combined momentum.

IV. Exploration

V. Understanding and Applying

2.5 Free Fall and Circular Motion Chapter 2 - Forces 2.5 Free Fall and Circular Motion

I. Essential Question: What is free fall? What is centripetal motion?

II. Key Vocabulary Free fall: when the only force acting on an object is gravity. Satellite: an object that orbits around other objects in space. Centripetal Force: a force that causes an object to move in a circular path.

III. Key Concepts Free fall is motion where the acceleration is caused by gravity. On Earth, objects have other forces, like air resistance acting on them. Without this, an object would move at 9.8 m/s after one second and 19.6 m/s after two seconds. But, with air friction/resistance, the velocity of an object remains below 9.8 m/s.

III. Key Concepts Some objects, like a baseball, fall to Earth in a curved pattern. The harder you throw the ball, the farther away from you it will land. A satellite follows this same idea, but because it is launched at a certain speed, it stays in orbit around the Earth instead of falling. Most satellites travel between 8,000-11,000 m/s; if they travel much slower than this they will fall to Earth, and if they travel faster than this they will escape into Space.

III. Key Concepts Satellites move in this circular pattern due to centripetal force. The force acts on the center of the object; if it were to be released from its orbit, then it will fly off in a straight line.

IV. Exploration

V. Understanding and Applying

Chapter 2 - Forces 2.6 Sinking and Floating

I. Essential Question: What makes an object float?

II. Key Vocabulary Buoyant force: water and other fluids exert an upward force on a submerged object.

III. Key Concepts Fluid pressure acts in all directions. It increases with depth, so there is a greater force at the bottom of an object than the top. It acts in the opposite direction of gravity, so it makes an object feel lighter.

III. Key Concepts Measure buoyant force by measuring the volume of the fluid that the object displaces. Two determine if an object will float, you can compare its density to the fluid’s density, or you can find the net force acting on the object.

III. Key Concepts If an object is more dense than the fluid around it, then it will sink. If an object is less dense than the fluid around it, then it will float. Density = mass / volume d = m/v

III. Key Concepts Buoyant force and floating: If the weight of the object is greater than the force, the object will sink. If the weight of the object is less than the force, the object will rise. If the weight and force are equal and not moving, the object will neither rise nor sink. Why would a boat that floats begin to sink?

IV. Exploration

V. Understanding and Applying