Motion
What things in the universe move? Everything….including the universe! Earth, the stars, and other objects all move with respect to one another.
Look at this book on the desk. Is it moving? YES! The book appears to be at rest, but it is moving relative to the Sun since Earth revolves around the sun.
Position A position is the location of an object. What is motion? Motion is a change in position over time.
Frame of Reference Positions and motions only make sense if you have a frame of reference. If I tell you that I am south, would anyone know where I was? No. In order to know my location, you would need to have a frame of reference. What am I south of??? A frame of reference is a group of objects from which you can measure a position or the motion.
Frame of Reference Almost anything can be a frame of reference. Grids make it easy to describe a positions and motions. Maps often use grids on top of them. Frames of reference can move. Different frames of reference see things differently. If you are in a car and it is moving, people on the outside of the car see you as moving. If you look out the window as the car is moving, things outside of the car appear to be moving.
How can you measure the distance an object has moved? Distance can be measured as the length of an arrow that is drawn from the old to the new position of the object.
How could you be moving in one frame of reference, but not in another? I could be at rest in one frame of reference, but all the objects in that frame of reference could be moving in relation to a second frame of reference. For example, I could be sitting at rest in a car while the car is moving. Everything outside the car would appear to be moving, but I would appear to be at rest.
What is the fastest vehicle you have traveled in? Car Train Airplane
When you travel, do you always move at a constant speed? No. The vehicle will speed up and slow down.
What is speed? Speed is how fast an object’s position changes over time. Calculating speed: Divide the distance traveled by the time spent traveling. If the distance traveled is 100m and the time traveled is 10 s, the speed is calculated by dividing 100 by 10. The answer is 10 m/s (10 meters per second. The term per means divide.)
What is velocity? Velocity is the measurement that combines both the speed and the direction of a moving object.
How do you calculate average speed? Divide the total distance traveled by the total time.
How are speed and velocity different? Speed is how fast an object’s position changes over time. Velocity combines speed with direction. For example, a car traveling at a speed of 15 mph might have a velocity of 15 mph west.
Acceleration Acceleration is the change in velocity over time for an object. When the velocity (speed and direction of a moving object) changes, it is accelerating. Acceleration has a direction. Accelerating happens when an object speeds up, slows down, or changes direction.
What is the direction of acceleration when traveling in a curve? The direction of acceleration moves toward the center of the curve.
Which would be more difficult…stopping a truck or a skateboard? Why? The truck (of course !) The truck has greater mass than the skateboard and thus greater momentum.
What is momentum? Momentum is the product of mass multiplied by velocity. The more momentum an object has, the easier it is for that object to move other objects.
What is inertia? Inertia is the tendency of any object to resist a change in motion or of a moving object to keep moving in a straight. The more mass an object has the more inertia an object has.
Who would be harder to stop- a professional hockey player skating at 4 m/s or a fifth-grader skating at 4 m/s? Why? The hockey player would be more difficult to stop because he or she would have the same velocity but more mass and momentum.
What changes the momentum of an object? Momentum changes when a change occurs in velocity or mass. An object can gain or lose mass, or it can accelerate.