b. Velocity tells you both speed and direction of an object s movement. Velocity is the change in position divided by the change in time.

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1 I. What is Motion? a. Motion - is when an object changes place or position. To properly describe motion, you need to use the following: 1. Start and end position? 2. Movement relative to what? 3. How far did it go? 4. In what direction did it go? b. Distance the length of the path or route traveled between two points, how far something moves c. Displacement the distance and direction along the shortest path an object has moved from its starting point Label the following line segments as distance or displacement. II. Speed and Velocity a. Speed the distance traveled divided by the time interval during which the motion occurred, calculated as distance divided by time s = d/t t = d/s d = s x t A bird is observed to fly 50 meters in 7.5 seconds. Calculate the speed of the bird in m/s. A race car travels 300km in 2 hours. What is the race car s speed? 1. Constant speed - the same change in distance is traveled every second. 2. Average speed found by dividing the total distance traveled by the time taken. 3. Instantaneous speed the speed of an object at one instant of time.

2 b. Velocity tells you both speed and direction of an object s movement. Velocity is the change in position divided by the change in time. III. Acceleration and Momentum a. Acceleration - the rate at which the velocity of an object changes with time, calculated as the change in velocity divided by time b. A change in velocity (acceleration) can be an increase in speed, decrease in speed, or a change in direction. 1. An increase in velocity is commonly called positive acceleration. 2. A decrease in velocity is commonly called negative acceleration, or deceleration. a = (s f s i ) / t A jet starts at rest at the end of a runway and reaches a speed of 80 m/s in 20 s. What is its acceleration? A skateboarder is moving in a straight line at a speed of 3 m/s and comes to a stop in 2 sec. What is his acceleration? c. Momentum describes the tendency of objects to keep going in the same direction with the same speed. Momentum = mass x velocity p = m x v A car is traveling at a velocity of 13.5 m/sec north on a straight road. The mass of the car is 1,300 kg. A motorcycle passes the car at a speed of 30 m/sec. The motorcycle (with rider) has a mass of 350 kg. Calculate and compare the momentum of the car and motorcycle. d. Law of conservation of momentum any time objects collide, the total amount of momentum is the same before and after the collision. Total p = p 1 + p 2 A train car moving to the right at 10 m/s collides with a parked train car. They stick together and roll along the track.

3 If the moving car has a mass of 8,000 kg and the parked car has a mass of 2,000 kg, what is their total momentum after the collision? What is the combined velocity of the trains after the collision? IV. Force a. Force any push or pull on an object resulting from an objects interaction with another object, measured in newtons (N) 1. Net force the combination of all the forces action on an object 2. Balanced forces When two or more forces exerted on an object and their effects cancel each other out, the motion of the object does not change. 3. Unbalanced forces When two or more forces act on an object and the net force is not zero, the motion of the object changes. +1 N -1 N + 1 N - 2 N +2 N +2 N b. Friction a force that resists motion between two surfaces that are touching each other 1. Three types of friction a. Static friction force caused by the attraction between the atoms on the two surfaces that are touching each other

4 b. Sliding friction force that is caused by two objects rubbing against each other c. Rolling friction force which opposes the motion of one object rolling over another 2. Reducing friction friction can wear down objects or resist motion to the point of not allowing parts to move, causing them to not function properly. To reduce friction, we can use lubricants. V. Newton s First Law of Motion a. Newton s first law of motion an object at rest remains at rest, and an object in motion remains in motion at a constant speed and in a straight line unless acted on by an unbalanced force. 1. Inertia tendency of objects to resist changes in motion 2. Newton s first law is sometimes called the Law of Inertia VI. Newton s Second Law of Motion a. Newton s second law of motion the acceleration of an object depends on the mass of the object and the amount of force applied 1. Mass the amount of matter something contains 2. Acceleration the rate at which the velocity of an object changes with time a = F net / m F = ma Two dogs play tug of war. Each dog exerts a force on the rope. The first dog (24) pulls with a force of 10N to the left and the second dog (32kg) pulls with a force of 12N to right. What is the net force? What is the acceleration of the dogs? What is the force necessary to accelerate 1,250kg car at a rate of 40m/s 2? VII. Gravity a. Gravity is the force of attraction between objects. 1. The bigger the mass of an object the bigger its force of gravity. 2. The sun has a very large mass, so exerts a large pull of gravity on everything in the solar system. 3. The sun's gravity holds the planets in orbit around it.

5 VIII. 4. The planets do not fall towards the sun because they are moving sideways at high speed. 5. Gravitational force = (G * m 1 * m 2 ) / (d 2 ) a. G is a constant equal to 6.67 x 10-8 dyne * cm 2 /g 2 Mass and Weight a. How are mass and weight different? To understand the differences we need to compare a few points: 1. Mass is a measurement of the amount of matter something contains, while Weight is the measurement of the pull of gravity on an object. 2. Mass is measured by using a balance comparing a known amount of matter to an unknown amount of matter. Weight is measured on a scale. 3. The mass of an object doesn't change when an object's location changes. Weight, on the other hand does change with location. b. To determine weight, we can substitute the acceleration of the gravitational force for acceleration F=mg (force = mass x acceleration of gravity) 1. On Earth, the acceleration of gravity (g) is equal to 9.8 m/s2 downward, which rounded is 10 m/s 2 downward 2. On the moon, = 1.6 m/s 2 3. On Venus, g = 8.83 m/s 2 4. On Jupiter, g = 26.0 m/s 2 1 newton = pounds force A girl has a mass of 42kg, what is her weight on Earth in N and pounds? What is her weight in N and pounds on the moon? Venus? Jupiter? IX. Newton s third law of motion a. Newton s third law of motion forces always act in equal but opposite pairs. For every action, there is an equal but opposite reaction.