F(16-1) How do forces affect us?

VocabularyVelocityForce

Accelerationinertia

Describing Motion• All motion is the same in

certain ways. All motion is change in position.

• You can tell that something has moved if it’s position changes relative to something else.

• A stationary object or a group of objects used to determine a position change is called a frame of reference.

• A frame of reference is a point of view. It can change depending on the viewer.

Describing Motion

• Speed is the distance something moves in a certain period of time.

• Speed = distance /time (km/hr).

• Speed tells how fast or slow an object’s motion is, but it doesn’t tell you the direction of motion.

Describing Motion

• When you state the direction of a moving object as well as its speed, you’re stating its velocity.

• Velocity = speed with direction.

• An object’s velocity changes when there’s a change in its speed, its direction, or both.

• Scientists use arrows to represent velocity. The length of the arrow represents the speed measurement. The direction it points represents the direction measurement.

What forces do

• A force is just a push or pull.• Gravity and magnetism are forces.• Forces act on objects. They slow things down,

speed them up, stop them, start them and turn them.

• Forces can change the object’s velocity.

What forces do

• Change of velocity is called acceleration.

• Acceleration is an object’s change in velocity divided by the time it takes for that change to occur.

What forces do

• Isaac Newton (1642-1727) is considered one of the greatest of all scientists.

• One of his laws states that the greater the force on an object, the greater its acceleration.

• This law also says that if two objects are acted on by the same force, the object with less mass accelerates more.

Inertia

• An object won’t change its motion unless a force acts on it.

• This tendency of matter to resist a change in its state of motion is called inertia.

• The law of motion (law of inertia): An object at rest stays at rest, and an object in motion stays in motion at a constant velocity, unless an object is acted on by an outside force.

• This means; an object will not accelerate unless a force acting on it.

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