Chapter 12: Forces and Motion
Section 12.1 – Forces
•A is a that acts on an object.
•A can cause a resting object to , or can ______a moving object by changing the object’s .
•The of the in a scale depends on the amount of (a type of force) acting on it.
• is measured in .
•One is the force that causes a mass to ______a rate of ______.
1N =
•You can use an to represent .
•The represents the and the represents the .
• is a .
• combine by .
• pointing in the direction ______together, and pointing in directions ______from one another.
•The is the force action on an object after all the forces are .
•Sometimes the acting on an object is .
•When the on an object are , the net force is and there is in the object’s motion.
•An is a force that results when the ______acting on an object is not equal to .
•When an acts on an object, the object ______.
•The equals the size of the force minus the size of the force.
•All objects are subject to , a ______that opposes the motion of objects that as they move past each other.
•There are four main types of friction: ______
______.
• is the friction force that acts on objects that are .
• always acts in the direction ______to that of the applied .
• is a force that opposes the direction of motion of an object as it over a surface.
•When a object rolls across a floor, the object and the floor are slightly.
•The change in shape when something rolls is the cause of ______, the friction force that acts on ______objects.
• are substances that like liquids and gases.
•The force of opposes the motion of an object through a .
• acting on an object moving through ____ is known as .
• is an force that acts between any two .
• does not require objects to be in for it to act on them.
•As objects to the ground, they and gain speed.
• causes objects to accelerate ______, whereas acts in the direction ______to the motion and acceleration.
•As the of a falling object , so does the .
• is the constant velocity of a ______when the force of air resistance equals the force of .
• is the curved path of a falling object after it is given an initial forward .
•The combination of an initial forward and the downward vertical force of causes the ball to follow a .
•An object that is and an object that is ______will strike the ground at the ______.
Section 12.1 Assessment
- How is the motion of an object affected when a force acts on it?
- List the four types of friction.
- How does air resistance affect the acceleration of a falling object?
- Earth’s gravitational force acts in what direction?
5.Compare the strengths of static, sliding, and rolling friction.
6.Explain why falling leaves often do not fall in a straight-line path to the ground.
7.Two coins are knocked off a table at the same time by different forces. Which coin will hit the floor first?
Section 12.2 – Newton’s First and Second Laws of Motion
- incorrectly proposed that is required to keep an object moving at ______.
- concluded that moving objects not subjected to or any other force would continue to move ______.
- According to , the state of motion of an object does not change as long as the ______acing on the object is .
• is the tendency of an object to change in its motion.
•An object at rest tends to , and an object in motion tends to with the same speed and .
•According to , the acceleration of an object is equal to the acting on it divided by the object’s .
• is the amount of an object contains.
a = acceleration =
acceleration (a) =
force (F) =
mass (m) =
Sample Problems
•A car with a mass of 1000kg accelerates when the traffic light turns green. If the net force on the car is 4000N, what is the car’s acceleration?
•A boy pushes a cart of groceries with a mass of 40kg. What is the acceleration of the cart if the net force is 60N?
•An automobile with a mass of 1200kg accelerates at a rate of 3m/s2. What is the net force acting on the car?
• is the amount of an object contains.
• is the force of acting on an object.
W = Weight =
Weight (W) =
mass (m) =
gravity (g) =
• is a measure of the of an object, ______is a measure of the force of acting on an object.
•On the , the acceleration due to gravity is about ______that of the Earth.
Section 12.2 Assessment
- State Newton’s first law of motion in your own words.
- What equation states Newton’s second law of motion?
- How is mass different from weight?
- Describe an example of Newton’s first and second laws that your observe in a normal day.
- A dummy’s mass is 75kg. If the net force on the dummy is 825N toward the rear of the car, what is the dummy’s deceleration?
Section 12.3 – Newton’s Third Law of Motion and Momentum
•A cannot exist . always exist in .
•According to , for every force there is an equal and .
•The force object A exerts on object B is called the ______.
•The force that object B exerts back on object A is called the ______.
• can produce like when a swimmer takes a stroke.
• sometimes produce ______like when you push against a wall.
•Action and reaction forces because although they are in different , they are also acting on .
• is the product of an object’s and its .
•An object with a is hard to .
•The for any object at is .
p =momentum =
momentum (p) =
mass (m) =
velocity (v) =
•According to the , if no acts on a system, then the ______of the system does not .
•In a closed system, the of one object equals the of another object.
Section 12.3 Assessment
- Using Newton’s third law, explain what is meant by action and reaction forces.
- State in your own words the formula for momentum.
- What is a necessary condition for the conservation of momentum?
- Explain how Newton’s third law of motion is at work when you walk.
- If an eagle and a bumblebee are traveling at 8km/hr, which has more momentum? Explain.
Section 12.4 – Universal Forces
•The four universal forces are the ______
______.
•All the act over a ______between particles of matter, which means that the particles do not need to be in with one another.
• force is associated with ______.
•Electric force and magnetic force are the only force that can both .
• act between charged objects or particles such as .
•Objects with charges while objects with charges .
• act on certain metals, on the poles of ______, and on moving charges.
•Two forces, the nuclear and the nuclear force, act within the to hold it together.
•The is a powerful force of attraction that acts only on the in the nucleus, holding them together.
•The nuclear force acts over very distances.
•The is an attractive force that acts over a range than the nuclear force.
• is an attractive force that acts between any two ______.
• states that every object in the universe every other object.
•The force between two objects is proportional to their and decreases as the ______between them increases.
• is the universal force, but it is the most effective over .
•A is a center-directed force that continuously changes the of an object to make it move in a .
•This force causes the to orbit the .
•The pull from the moon produces two ______in Earth’s oceans.
•These produce the high and low ______each day.
Section 12.4 Assessment
- Which universal force can repel as well as attract?
- Which universal force acts to hold the nucleus together?
- State in your own words what is meant by Newton’s law of universal gravitation.