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Chapter 12 Forces and Motion
The Physics Classroom Tutorial: Newton’s Laws; The Physics Classroom Multimedia: Newton’s Laws
Chapter 12 Vocabulary Worksheet
12.1 Forces
12.1.1 Describe examples of force & identify appropriate SI units used to measure force.
12.1.2 Explain how the motion of an object is affected when balanced and unbalanced forces act on it.
12.1.3 Compare & contrast the four kinds of friction.
12.1.4 Describe how Earth’s gravity and air resistance affect falling objects.
12.1.5 Describe the path of a projectile and identify the forces that produce projectile motion.
- A force can cause a resting object to move, or it can accelerate a moving object by changing the object’s speed or direction.
- When the forces on an object are balanced, there is no change in the object’s motion. When an unbalanced force acts on an object, the object accelerates.
- There are four main types of friction: static friction, sliding friction, rolling friction, and fluid friction.
- Earth’s gravity acts downward toward the center of Earth. Gravity causes objects to accelerate downward, whereas air resistance acts in the direction opposite to the motion and reduces acceleration.
- The combination of initial forward velocity and downward vertical force of gravity cause a projectile to follow a curved path.
force – a push or pull that acts on an object
newton – (N) The SI unit for force that causes a 1-kilogram mass to accelerate at a rate of 1 meter per second squared (1N = 1kg∙m/s2)
net force – the overall force acting on an object after all the forces are combined
friction – a force that opposes the motion of objects that touch as they move past each other
static friction – a friction force that acts on objects that are not moving
sliding friction – a friction force that opposes the motion of an object as it slides over a surface
rolling friction – a friction force that acts on rolling objects, caused by the change in shape at the point of rolling contact
fluid friction – a friction force that opposes the motion of an object through a fluid
air resistance – fluid friction acting on an object moving through the air
gravity – the attraction between any two objects because of their masses
terminal velocity – the constant velocity of a falling object when the force of air resistance equals the force of gravity
projectile motion – the curved path of an object in free fall after it is given an initial forward velocity
12.1 PowerPoint (40 slides) & Note Guide
Mrs. Griffin Introduction to Forces
Mrs. Griffin Forces Balanced & Unbalanced
Mrs. Griffin Newton’s Laws: One, Two, Three
Brightstorm: Force (3:50) A force is defined in physics as anything that affects an object's acceleration. A force is a vector quantity because it has both magnitude and direction. The unit for force is the Newton (N) or kg/ms^2
Brightstorm: Gravity Overview (4:25) All objects with mass attract and are attracted by all other objects with mass because of a force called gravity. The strength of gravity is proportional to the mass of the object. We are pulled to the Earth by it's gravitational forces but we also pull the earth towards us. Because we are much less massive than the Earth, our gravitational pull is not strong enough to have any affect on it. Gravity pulls us towards Earth such that we accelerate at 9.8 m/s^2.
**http://www.woodlands-junior.kent.sch.uk/revision/Science/physical.htm – nice mini lesson & activities
**http://pbskids.org/sid/funwithfriction.html – more for younger kids, entertaining nonetheless
http://fearofphysics.com/Friction/friction.html - do an experiment with friction & braking, changing variables
Sunburst Friction Video (17:41)
Sunburst Gravity Video (16:53)
12.2 Newton’s First and Second Laws of Motion
12.2.1 Describe Newton’s first law of motion and its relation to inertia.
12.2.2 Describe Newton’s second law of motion and use it to calculate acceleration, force, and mass value.
12.2.3 Relate the mass of an object to its weight.
- According to Newton’s first law of motion, the state of motion of an object does not change as long as the net force acting on the object is zero.
- According to Newton’s second law of motion, the acceleration of an object is equal to the net force acting on it divided by the object’s mass.
- Acceleration = Net Force / Mass.
- Weight = Mass x Acceleration due to gravity.
- Mass is a measure of the inertia of an object; weight is a measure of the force of gravity acting on an object.
inertia – the tendency of an object to resist a change in its motion
mass – the amount of matter in an object; a measure of the inertia of an object, which depends on the amount of matter the object contains
weight – the force of gravity acting on an object
12.2 PowerPoint (45 slides) & Note Guide
Brightstorm: Law of Inertia - Newton's First Law of Motion (1:30) According to Newton’s First Law of Motion, also known as the Law of Inertia, an object at rest remains at rest and an object in motion remains in motion until it is acted upon by an unbalanced force.
Brightstorm: Law of Force and Acceleration - Newton's Second Law of Motion (2:11) According to Newton’s Second Law of Motion, also known as the Law of Force and Acceleration, a force upon an object causes it to accelerate according to the formula net force = mass x acceleration. So the acceleration of the object is directly proportional to the force and inversely proportional to the mass.
Investigation 12A Using a Pendulum to Measure Acceleration Due to Force of Gravity
Investigation 12B Testing Galileo’s Hypthesis
12.3 Newton’s Third Law of Motion and Momentum
12.3.1 Explain how action and reaction forces are related according to Newton’s third law of motion.
12.3.2 Calculate the momentum of an object and describe what happens when momentum is conserved during a collision.
- According to Newton’s third law of motion, forces exist as equal and opposite force pairs.
- Momentum = Mass x Velocity; An object has a large momentum if the product of its mass and velocity is large.
- Momentum is conserved in a closed system.
momentum – the product of an object’s mass and its velocity
law of conservation of momentum – law stating that the total momentum of a system does not change if no net force acts on the system
12.3 PowerPoint (31 slides) & Note Guide
Exploration Lab Investigating a Balloon Jet
Brightstorm: Net Force- Resultant Force (1:18) The Newton's Third Law of Motion states that for every action there is an equal and opposite reaction. Simply put, it means that every force can be undone. Mathematically, it means that for every vector there is another vector with opposite direction and equal magnitude.
Brightstorm: Law of Action and Reaction - Newton's Third Law of Motion (1:18) The Newton's Third Law of Motion states that for every action there is an equal and opposite reaction. Simply put, it means that every force can be undone. Mathematically, it means that for every vector there is another vector with opposite direction and equal magnitude.
Brightstorm: Conservation of Momentum (5:54) The law of conservation of momentum says that if two objects collide, the force lost by one object is equal to the force gained by the other object. The total momentum of the system is the same after the collision as before it as shown by the equation initial momentum = final momentum (where final momentum is the sum of all momentums present in the system). This principle is similar to the law of conservation of energy.
12.4 Universal Forces
12.4.1 Identify the forms of electromagnetic force that can both attract and repel.
12.4.2 Identify and describe the universal forces acting within the nucleus.
12.4.3 Define Newton’s law of universal gravitation and describe the factors affecting gravitational force.
12.4.4 Describe centripetal force and the type of motion it produces.
- Electric and magnetic forces are the only forces that can both attract & repel.
- The strong and weak nuclear forces hold the nucleus together.
- Newton’s law of universal gravitation states that every object in the universe attracts every other object.
electromagnetic force – a force associated with charged particles, which has two aspects, electric force and magnetic force
strong nuclear force – the powerful attractive force that binds protons and neutron together in the nucleus
weak nuclear force – a powerful attractive force that acts over a short range
gravitational force – an attractive force that acts between any two objects
centripetal force – a force that continuously changes the direction of an object to make it move in a circle
12.4 PowerPoint (31 slides) & Note Guide
Brightstorm: Centripetal Force (4:10) Centripetal force causes an object in motion to continue in a curved path rather than a linear one. If this force stops, the object will continue in a tangential linear path. An example of centripetal force is how planets rotate around the sun. In this case gravity is a centripetal force because it keeps the planets on curved paths and we say that centripetal acceleration = velocity^2 /radius while centripetal force = mass x velocity^2 / radius.
cffquaker – short review PowerPoint & Jeopardy Review
Sunburst Forces Video Quiz (30:46)
