Forces

Log into my website, click the Introduction to Forces Notes On a note card, define the following terms: Force Newton Unbalanced force Contact force (give examples) Applied force Normal force Friction Tension Mass Weight

Forces A FORCE is a push or a pull exerted on an object Forces cause objects to speed up, slow down, or change direction. Force is measured in Newtons

Force Forces come in pairs A force is a vector Forces have a magnitude and a direction 5N, north (up) Magnitude: 5N Direction: north (up)

Types of Forces There are two types of forces Contact forces Forces at a distance (long-range)

Contact Forces Contact forces- types of forces that result when the two interacting objects are perceived to be physically contacting each other Examples of contact forces: 1. Applied force 2. Friction force 3. Tension force 4. Normal force 5. Air resistance

Applied Force Identified as F a Applied to an object by a person or another object Acts in the horizontal direction, parallel to the surface

Friction Force Identified as F f Acts opposite sliding motion between surfaces Acts in the horizontal direction, parallel to the surface and opposite the direction of sliding

Tension Force Identified as F T Pull exerted by a rope, string, or cable attached to a body and pulled tight Acts away from the object and parallel to the string, rope or cable

Normal Force Identified as F N Exerted by a surface on an object (presses two surfaces together) Acts in an upward, vertical direction, perpendicular to the surface Sometimes referred to as the support force

Air Resistance Force Identified as F air Type of frictional force that acts upon objects as they travel through the air Acts opposite motion

Long Range Forces Long Range Forces- types of forces that result even when the two interacting objects are not in physical contact with each other, yet are able to exert a push or pull despite their physical separation Examples of long range forces: 1. Gravitational force 2. Electrical force 3. Magnetic force

Gravitation al Force All objects on Earth experience a force of gravity that is directed downward towards the center of the earth. Identified as F W Referred to as the force of weight Acts in the vertical direction

Balanced and Unbalanced Forces Forces occur in pairs and they can be either balanced or unbalanced

Balanced Forces Balanced forces do not cause change in motion, they are in equilibrium They are equal in size and opposite in direction

Unbalanced Forces An unbalanced force always causes a change in motion Forces are not in equilibrium When unbalanced forces act in opposite directions you can find the net force The net force is the sum of all the forces acting on an object

Unbalanced Forces 4 N, left – 10 N, right = 6N, right

Unbalanced Forces 3 N, right – 6 N, left = 3N, left

Bellwork Pick up notes/activity sheet from the front Answer the review questions at the top

Net Force A net force shows magnitude and direction The magnitude is the difference between forces acting on an object The resulting motion of an object is in the direction of the largest force

Balanced Forces Balanced forces cause no change in motion. This can happen when the object is not moving or when the object is moving with constant velocity.

Unbalanced Force Unbalanced force means that the force applied in one direction is greater than the force applied in the opposite direction. When unbalanced forces are acting on an object, there is a change in speed and direction.

Arm wrestling

Force Body (free body) Diagrams Used to show all the forces acting on an object (can be 1,2,3, or 4 forces) Can help you understand the motion of an object Force vectors are represented by arrows The length of the arrow represents the magnitude (size) of the force

How to Draw a Force Body Diagram (page 1) Step 1: Draw a sketch of the situation (page 2) Step 2: Identify the horizontal forces (page 3) Step 3: Identify the vertical forces (page 4) Step 4: Draw a box, place a dot in the middle (page 5) Step 5: Draw and label the horizontal forces (page 6)

How to Draw a Force Body Diagram Step 6: Draw and label the vertical forces Step 7: Calculate the sum of all the forces

Example A book is at rest on a tabletop. Diagram the forces acting on the book.