Forces & Motion Forces

Forces are acting all around you. Forces are acting all around you. Objects, including you, are being pushed and pulled in different directions. Objects, including you, are being pushed and pulled in different directions. Sometimes forces cause motion: Sometimes forces cause motion: –sliding a chair, throwing or kicking a ball, pushing a grocery cart More importantly, stationary objects (objects sitting still) have forces acting on them too More importantly, stationary objects (objects sitting still) have forces acting on them too –a pop can on the counter, a picture frame on the wall, computer on the desk

Objects exert forces on each other: Objects exert forces on each other: –You are exerting a force on your chair, AND you chair is exerting a force equally on you. Forces have magnitude and strength. Forces have magnitude and strength. Strength is measured in Newtons (named after Sir Isaac Newton) Strength is measured in Newtons (named after Sir Isaac Newton)

Forces affect objects in several ways… Forces affect objects in several ways… –Forces acting on stationary objects can set the object in motion (wind = forces that blows over a trash can). –Forces can change a moving object’s speed and or direction it’s moving (you get hit in the head with a ball – your head (outside force) changes the direction and speed that the ball was going). –A force can affect an object without making it move (balanced forces) –Forces can change a stationary object’s shape (squeezing a balloon)

Gravity is a force. Gravity acts on all objects that have mass. Gravity acts on all objects that have mass. All objects have mass. All objects have mass. The strength of gravity depends on two things: The strength of gravity depends on two things: –The mass of the object. –The distance between two objects. Mass is the measure of the amount of ‘stuff’ inside an object Mass is the measure of the amount of ‘stuff’ inside an object The greater the mass of either object, the stronger the gravity between them. The greater the mass of either object, the stronger the gravity between them.

Friction is a force Friction is a force that opposes motion between two surfaces that are in contact with each other. Friction is a force that opposes motion between two surfaces that are in contact with each other. –Friction may prevent motion from starting, it may slow motion down, it may even stop it When two solid surfaces slide against each other, it is known as sliding friction. When two solid surfaces slide against each other, it is known as sliding friction. When two solid surfaces roll over one another, it is known as rolling friction. When two solid surfaces roll over one another, it is known as rolling friction.

When a solid surface passes through air or water, it is known as fluid friction. When a solid surface passes through air or water, it is known as fluid friction. Friction depends on two things: Friction depends on two things: –The type of surfaces involved. –How hard the surfaces are pressing on one another.