Motion, Forces and Simple Machines

Chapter 5

Section 1- Motion

• Instantaneous Speed:– The speed of an object at any instant of time is the

instantaneous speed!• How is instantaneous speed different from

average speed?– Instantaneous speed is speed at any instant whereas

average speed is speed over a time interval (period of time).

• Constant Speed:– When the instantaneous speed of an object is the

same at any time, the object is going at a constant speed. In other words, the speed is the same throughout time!

Section 2- Newton’s Laws of MotionForce:

- A force is a push or pull. - The SI unit used to measure force is the Newton (N)- 1 Newton (N) is equal to 1 kg x m/s2

Force and Acceleration- For an object’s motion to change, a force must be

applied to the object- A force can also change an object’s direction.- Gravity is type of force that exist on Earth and always

affects objects that are in motion- Anytime an object’s speed, or direction of motion, or

both change, a force must have acted on the object

• Balanced Forces:– When two or more forces act on an object and their effects

cancel out.– They do not cause a change in an object’s motion

• Unbalanced Forces:– When two or more forces act on an object and their effects DO

NOT cancel out.– They cause a change in an object’s motion

• Net Force:– Net force is the combination of all forces acting on an object

• When two or more forces act in the same direction on an object, the net force is the sum of the forces

• When two forces of equal force act on an object, in the opposite direction, they cancel out and we have a net force of 0.

• When two unequal forces act in opposite direction on an object, you find the net force by calculating difference between the two forces

• Newton’s Laws of motion are a set of principles used to explain the motion of objects.

• Newton’s First Law states that an object in motion will stay in motion, or an object at rest will stay at rest unless an unbalanced force acts on it

• Friction is a force between two surfaces in contact that resists the motion of the surfaces past each other. Friction always acts in the opposite direction of motion.

• Inertia is the tendency of an object to resist a change in motion– Relationship between mass and inertia:

• The more mass an object has, the greater its inertia– Mass measures the quantity of matter

Section 3- Work and Simple Machines

• Work is done when a force causes an object to move in the same direction as the force that is applied. Work is measured in Joules (J) which is equivalent to (N x m)– For work to be done, you must apply force to an

object and the object must move in the same direction as the force you apply.

– Work (in J) = force (N) x distance (m) • [W = Fd]

• The Pulley is an object, like a wheel, that has a groove with a rope or cable running through it. – A pulley changes the direction of the input force to make

work easier.– Mechanical advantage of a pulley is 1– Mechanical advantage of a double pulley is 2

• The lever is a rod or plank that pivots around a fixed point called the fulcrum.– 1st class levers: fulcrum is between output force and input

force. Used to increase force.– 2nd class levers: output forces is between input force and

fulcrum. Output force is always greater than input force.– 3rd class levers: input force is between output force and

fulcrum. Increases the distance over which the input force is applied.

• The wheel and axle is made of two round objects that are attached and rotate together about the same axis. – Calculate Mechanical advantage by dividing the

radius of wheel by the radius of the axle.• How do the lever, pulley, and wheel and axle

make work easier?– A lever increases the input force or the distance

over which the force is applied. A pulley changes the direction of the input force and can increase it. A wheel and axle increases the input force and changes its direction.

• The inclined plane is a sloped surface, sometimes called a ramp.– it allows you to lift heavy loads by using less force

over a greater distance– To calculate mechanical advantage of an inclined

plane, you divide the length of the inclined plane by its height

• The wedge is a moving inclined plane with one or two sloping sides.– It can change the direction of the input force

• The screw changes the direction of the force you apply