MOTION & FORCES SPS8. STUDENTS WILL DETERMINE RELATIONSHIPS AMONG FORCE, MASS, AND MOTION. A. CALCULATE VELOCITY AND ACCELERATION. B. APPLY NEWTON S THREE LAWS TO EVERYDAY SITUATIONS BY EXPLAINING THE FOLLOWING: INERTIA RELATIONSHIP BETWEEN FORCE, MASS AND ACCELERATION EQUAL AND OPPOSITE FORCES C. RELATE FALLING OBJECTS TO GRAVITATIONAL FORCE D. EXPLAIN THE DIFFERENCE IN MASS AND WEIGHT.
FIRST, WHAT IS MOTION? Motion is the change in or. Motion involves and. The reference frame is the stationary background. There must be something that is not moving so that you can tell that the object changed positions Motion has components:,, and.
SPEED A THING OF THE PAST! Just so you know: by definition it s how fast an object. In order to determine speed, you must have and. You must know how far the object moved and how long it took for it to move. In order to calculate speed, we divide. The main (SI) units for speed are (m/s) Speed can also be expressed as km/h or mph Speed calculations are averages. In physics, objects motion will be described with velocity
VELOCITY GRAPHS Speed can be represented on a graph The graph has time on the x axis and distance on the y axis 80 70 60 50 40 30 20 10 Corvette Porshce Lamborghini 0 0 sec 1 sec 2 sec 3 sec 4 sec 5 sec
VELOCITY Velocity is basically the same as speed with one additional component! You still calculate velocity the same as speed, however, you must add a direction to your final answer.
HOW IS MOMENTUM DIFFERENT FROM VELOCITY? is a quantity defined as the product of an object s mass and its velocity In other words momentum is * The symbol for momentum is p
MOMENTUM Which has more momentum, a 1000 kg car moving 1 m/s or a 70 kg person sprinting at 8 m/s?
WHAT IS ACCELERATION? is the change in velocity divided by the time interval in which the change occurred. In other words, acceleration = final velocity-initial velocity a = Δv t time
ACCELERATION Acceleration can be positive or negative If positive, the object is speeding up; If negative, the object is slowing down. If acceleration is zero, velocity is constant.
FORCE is the cause of acceleration, or change in an object s velocity. A force can be a or a to change motion or the total of all forces acting on an object, determines whether the velocity of the object will change. The object will accelerate in the direction of the net force. If the net force is zero, the object won t accelerate.
FORCES do not change motion. The net force is zero. With unbalanced forces, one force is greater than the other. Force is measured in newtons (N) (We ll talk more about this later!) But 1 N = 1 kg * 1 m/s 2
Some Examples from Real Life A soccer ball is sitting at rest. It takes an unbalanced force of a kick to change its motion. Two teams are playing tug of war. They are both exerting equal force on the rope in opposite directions. This balanced force results in no change of motion. NSF North Mississippi GK-8
FRICTION is a force between two objects in contact that opposes the motion of either object In other words, friction causes an object to slow down or stop
FRICTION There are 4 major types of friction : Friction that tends to keep an object at rest : Friction that occurs when objects slide over each other : Friction that is produced by rolling objects, such as wheels or ball bearings : Friction that is exerted on an object by fluids to slow it down air resistance!
AIR RESISTANCE Air resistance is a form of. It is the air molecules acting on the surface of the object. Air resistance depends on size and shape. What object has undergone the most changes to counteract air resistance? The automobile.
GRAVITY is the attraction between two particles of matter due to their mass. Gravity is affected by and. The greater the mass, the greater the gravitational forces it exerts on other objects The earth is larger than the person sitting next to you.that s why your feet are on the earth s surface and not on your classmate.
SIR ISAAC NEWTON Newton was one of the most influential scientists of the seventeenth century. He discovered three basic laws that explain all aspects of motion. His laws govern all motion! There are three laws.
NEWTON S FIRST LAW OF MOTION States that objects at rest tend to stay at rest, and objects that are moving tend to continue moving. This tendency of objects to resist changes in motion is called. Basically, an object will keep doing what it was doing unless acted on by an. If the object was sitting still, it will remain stationary (still). If it was moving at a constant velocity, it will keep moving. It takes to change the motion of an object.
More Examples from Real Life A powerful locomotive begins to pull a long line of boxcars that were sitting at rest. Since the boxcars are so massive, they have a great deal of inertia and it takes a large force to change their motion. Once they are moving, it takes a large force to stop them. On your way to school, a bug flies into your windshield. Since the bug is so small, it has very little inertia and exerts a very small force on your car (so small that you don t even feel it). NSF North Mississippi GK-8
If objects in motion tend to stay in motion, why don t moving objects keep moving forever? Things don t keep moving forever because there s almost always an unbalanced force acting upon it. A book sliding across a table slows down and stops because of the force of friction. If you throw a ball upwards it will eventually slow down and fall because of the force of gravity. NSF North Mississippi GK-8
In outer space, away from gravity and any sources of friction, a rocket ship launched with a certain speed and direction would keep going in that same direction and at that same speed forever. NSF North Mississippi GK-8
NEWTON S SECOND LAW OF MOTION Newton's second law of motion states that when an unbalanced force is applied to an object the object accelerates. Simply put, force = *
So, what does this mean? Force is directly proportional to mass and acceleration. Imagine a ball of a certain mass moving at a certain acceleration. This ball has a certain force. Now imagine we make the ball twice as big (double the mass) but keep the acceleration constant. F = ma says that this new ball has twice the force of the old ball. Now imagine the original ball moving at twice the original acceleration. F = ma says that the ball will again have twice the force of the ball at the original acceleration.
IN OTHER WORDS If you double the mass, you double the force. If you double the acceleration, you double the force. What if you double the mass and the acceleration? (2m)(2a) = 4F Doubling the mass and the acceleration quadruples the force. So... what if you decrease the mass by half? How much force would the object have now?
MORE ON NEWTON S 2 ND LAW Something very massive (high mass) that s changing speed very slowly (low acceleration), like a glacier, can still have great force. Something very small (low mass) that s changing speed very quickly (high acceleration), like a bullet, can still have a great force. Something very small changing speed very slowly will have a very weak force.
NEWTON S THIRD LAW OF MOTION Newton's third law of motion states that for every force there is an equal and opposite force. These forces are called forces and forces. For every force acting on an object, there is an equal force acting in the opposite direction. Right now, gravity is pulling you down in your seat, but Newton s Third Law says your seat is pushing up against you with equal force. This is why you are not moving. There is a balanced force acting on you gravity pulling down, your seat pushing up.
Think about it... What happens if you are standing on a skateboard or a slippery floor and push against a wall? You slide in the opposite direction (away from the wall), because you pushed on the wall but the wall pushed back on you with equal and opposite force. Why does it hurt so much when you stub your toe? When your toe exerts a force on a rock, the rock exerts an equal force back on your toe. The harder you hit your toe against it, the more force the rock exerts back on your toe (and the more your toe hurts). NSF North Mississippi GK-8
FREE FALL & WEIGHT is the motion of a body when only the force of gravity is acting on it. Think about the ride at Six Flags Weight is equal to mass times free-fall acceleration. Free-fall acceleration is. Do not confuse weight and mass! Remember that mass is a measure of how much matter an object contains. Weight is the gravitational pull based on the object s mass.
TERMINAL VELOCITY Terminal velocity is the maximum velocity reached by a falling object that occurs when the resistance of the medium is equal to the force due to gravity Simply, it s the velocity at which the driving forces (pushing downward) are cancelled out by the resistive forces (pushing upward). Terminal velocity depends a great deal upon the shape of the object that is facing the direction it is moving. Once an object has reached terminal velocity, the object is not accelerating (a=0), therefore it is not speeding up or slowing down. It is a constant velocity unless the driving forces (pushing downward) or the resistive forces (pushing upward) change. Terminal Velocity Video
ONCE AGAIN, Simply stated Newton's three laws of motion are: An object moving in a straight line will keep moving in that direction unless acted on by an outside force. If an object is moved by a force, it will move in the direction of the force. Also the greater the force, the faster the object moves. For every action there is an equal and opposite reaction. Newton's 3 Laws