Understanding Forces in Science

• In science, force is defined as a push or a pull exerted by one object on another.
• The unit for force is the newton (N), equivalent to 1 kg⋅m/s².
• Force is a vector quantity, possessing both direction and magnitude.

Identifying Forces

• Weight refers to the gravitational force acting on an object.
• Mass is the measure of the amount of matter, which can be found using a balance.
• Mass is not a force.
• Spring scales measure weight and other forces via the pushing or pulling of a spring.
• Normal force is a supporting force exerted perpendicular to a surface.

Types of forces descriptions

• Air resistance: Air exerts a force against the moving box in a way that increases with the box's speed.
• Friction: force produced when two sliding surfaces act opposite to one another relative motion to the surfaces.
• Gravitational force: Earth exerts a force of attraction.
• Normal force: Object exerts a force on another object in a direction of perpendicular contact.

Exploring Friction

• Friction opposes motion between two surfaces in contact, arising from small points pushing against each other.
• Static friction occurs when surfaces are not sliding relative to each other, such as a box on a ramp.
• Kinetic friction resists motion when surfaces are sliding.
• Kinetic friction is generally less than the maximum static friction.
• Unlike air resistance, static and kinetic friction typically do not vary with speed or contact area.
• Friction is proportional to the normal force, which pushes the surfaces together and is perpendicular to the surface.

Using Diagrams to Analyze Force

• Normal force and static friction typically oppose other forces.
• When forces acting in the same direction produce a greater force.
• Forces combine as vectors.

Free-Body Diagrams

• Free-body diagrams model forces acting on a single object.
• Forces are represented as vectors acting from the object's center of mass.

Determining Net Force

• Net force (Fnet) is the vector sum of all external forces on an object, also written as ΣF.
• When forces are balanced, the net force is zero, resulting in no net effect on the object.

Forces in One and Two Dimensions

• Forces in one dimension can be represented as positive or negative numbers.
• Forces in two dimensions are analyzed separately in perpendicular directions.
• Coordinate systems can be oriented to align with frictional and normal forces.
• Normal force on a horizontal surface at rest equals the object's weight.
• Normal force on a slanted surface equals the component of gravity perpendicular to the surface.