Force Force Is a push or pull exerted

Force

Force: • Is a push or pull exerted on an object in order to change the motion of an object. • Described by its strength and the direction in which acts. • Has size and direction • Can change acceleration of an object • Not all force leads to movement (ex: the chair you sit in) To find force: Force = mass x acceleration • Force is measured in Newton (N)

• Net force: – Is the total of all forces working on an object. • If the forces are going in the same direction, we add the forces together. • If the forces are going in opposite directions, we subtract the forces. –The result net force is always in the direction of the larger velocity.

• Forces may cancel each other out and produce no net force. • Try this! – What is the net force being displayed in this picture?

There are 2 types of forces: 1. Balanced forces: • When the net force on an object is zero. • Produces no change in the motion of an object. – An object that is not moving will stay motionless – An object in motion will maintain speed & direction.

2. Unbalanced forces: • When the net force on an object is greater than zero. • Produce a change in the motion of an object. – Motionless object will begin to move – Object in motion change its speed &/or direction

Friction – Is the force that opposes motion between two surfaces in contact with each other. • Friction can – Prevent motion from starting – Oppose motion in progress (cause things to slow down or stop) Flat wheels don’t work. Too much Friction. Duh!!

• Source of friction – Occurs because the surfaces of any object is rough – Microscopic hills and valleys of both objects stick together, this contact causes friction. • Amount of friction depends on two things 1. Type of surfaces 2. How much force is pressing the two objects against each other.

– The larger the force between the two objects, the more friction you have – The smaller the force between the two objects, the less friction you have. Smaller Force Larger Force

Three types of friction 1. Kinetic Friction • “moving” friction-between moving surfaces – Sliding friction: » Opposes the movement of objects across each other (ex: brakes on your bike)

– Rolling Friction: » Friction between wheels on an object & the floor or ground. » Is usually has less force than sliding friction

2. Static Friction • “not moving” • When force is applied to an object, but does not cause it to move • Disappears once object starts to move by applying a big enough force

3. Fluid friction • Friction between water and an object – Example: walking on a wet floor. The friction is between your feet & the water not your feet and the floor. • Friction between air and an object acts in the same way as friction between water and an object

Can we use friction? YES!! • Helpful ways: – Tires push against the ground to move the car – Breaks use sliding friction to stop the car – Enables you to write with the friction between paper & pencil – Enables you to walk (friction between your feet and the ground)

• Harmful ways: –Cause high temperature in engine parts, causing a break down –Puts holes in your socks & jeans –Causes erosion of top soil

• Decrease or Reducing Friction – 3 Ways 1. Using lubricants » Examples: oils, wax, and grease 2. Switching from sliding to rolling friction 3. Making surfaces smoother • Increasing friction – 2 ways 1. Make surface rougher 2. Increase forces pushing surfaces together