How do you know something is moving?
An object is in motion if its position changes when compared to another object A reference frame is a place or object used for comparison to determine whether something is in motion Something fixed to the earth like a tree or stop sign are great reference frames
Because motion is determined by a reference frame that can change, motion is relative What if you are in a boat? Relative to the sun you are moving, but relative to the Earth you are sitting still
How Forces Affect Motion
The motion of an object can change when one or more forces act on the object A force is a push or pull When one object pushes or pulls another object, the first object exerts a force on the second object You exert a force on your book when you push it into your backpack
What force are you exerting right now?
A force is described by its strength and by its direction in which it acts The force needed to lift a dinner plate requires less strength than the force needed to push a refrigerator Pushing a faucet handle to the left is a different force than pushing the handle to the right The unit for the strength of a force is called a newton (N), named after the scientist Isaac Newton
What is a force? Give one example of a force that is constantly being exerted
Types of Forces
Forces are classified as either contact or noncontact Contact forces occur when two things touch Friction is a contact force that is exerted on both objects when they rub together A noncontact force is a force that occurs even if nothing is touching Gravity is a noncontact force that pulls objects towards each other as a result of their masses
Which activity exerts force?
- Jump Rope
- Riding a bik
Balanced & Unbalanced Forces
More than one force can act on an object If two forces are exerting equal amounts of strength in opposite directions this is said to be a balanced force When forces on an object are unbalanced there is net force acting on the object The net force on an object is the combination of all forces acting on that object
The speed of an object is the distance an object moves per unit of time Speed is a type of rate A rate tells you the amount of something that changes in one unit of time
Draw a pancake with superpowers flying through the sky
Distance Over Time
To calculate the speed of an object, divide the distance the object travels by the amount of time it takes to travel that distance Speed= Distance/Time
Calculate the speed with a distance of 8 miles and a time of 4 seconds
To describe an object's motion, you also need to know its direction The speed at which an object travels in a given direction is called velocity
Velocity & Airplanes
Air traffic controllers must keep close track of the velocities of aircrafts These velocities change as airplanes move overhead and on the runways An error in determining a velocity, either in speed or direction, could lead to a collision
What is the formula for calculating speed?
Speed and velocity are not the only ways to describe motion Scientists define acceleration as the rate at which velocity changes Velocity: the speed at which an object travels in a given direction A change in velocity can involve a change in speed, direction, or both In science, when an object accelerates, it changes speed or changes direction
Remember that any object in motion has energy of motion What happens in collisions? One way to look at it is a transfer of energy The car that hits the other transfers its energy to the other car