# Forces - Weebly FORCES Chapter 7 LEARNING OUTCOMES Define forces and different types of forces (push or pull) Measuring forces in Newtons Balanced vs unbalanced forces Inertia- what is it and how does it apply to Newtons first law of motion.

WHAT ARE FORCES? A force is a push, pull or twist that can change an objects motion WHAT CAN FORCES DO? Acceleration: increase in

speed Deceleration: decrease in speed MEASURING FORCES Force is measured using a unit called newtons (N)

The ability of springs to stretch and squash allow a weight force to be measured The larger he pulling force, the more the string is stretched, the higher the force

SUMMARY Not moving Speed BALANCED FORCES The downward force of gravity is balanced by the upward support force

from the chair. The forces acting on this person are balanced This is an example of an object that is not moving/stopped Note that the arrows are the

same length This is an example of an object travelling at the same speed without changing directions BALANCED FORCES

The forward force from the pedalling is cancelled out by the friction force pushing backwards forward force The forces at this stage are balanced

Note that the arrows are the same length UNBALANCED FORCES Motion will change when the forces are

unbalanced Forces are unbalanced when: oStart moving (pedalling fast and hard) oSpeed up (pedalling fast and hard) oSlows down (using the brakes) oComes to a stop (using the brakes) oChanges direction (turning the handle bars) UNBALANCED FORCES

Note that the arrows are now different lengths FORCES ACTING ON A

PLANE BUOYANCY Buoyancy is the upward force on an object that is produced by a surrounding gas or liquid, such as water. Archimedes figured out that if the weight of the object being placed in the water is less that the weight

of the water displaced, the object will float. This is known as buoyancy or the Archimedes principle. FORCES ACTING ON A BOAT

Buoyancy Drag/Air resistance Thrust Weight/

Gravity UNBALANCED FORCES SUMMARY Accelerate Arrow is larger therefore moving forward

Decelerate Arrow is larger therefore moving backwards Drag from caravan QUESTION

Driving Force (thrust) 1. State which direction the car is moving 2. Predict what would happen to the speed of the car if the caravan gained extra weight 3. If the car is travelling at a constant speed. Compare the size of the thrust and drag forces acting on the car Drag from

caravan Driving Force (thrust) 1. State which direction the car is moving To left or forward 2. Predict what would happen to the speed of the car if the caravan gained extra weight Decrease as the drag from the caravan will increase

3. If the car is travelling at a constant speed. Compare the size of the thrust and drag forces acting on the car The thrust balances the drag. No overall force is acting. (Balanced forces = Constant Speed) INERTIA Inertia is an objects resistance to changing its state of motion. The greater the mass of the object the greater the

inertia. Therefore the greater the mass and inertia the harder and more force is required to change the objects state of motion. INERTIA The tendency of an object to resist any change in its motion (unless a force is acted upon it)

If you put your school bag down, it will stay there until something happens to it Someone could lift it, push it or pull it to make it move. When left alone, the bag will not move NEWTONS LAW OF MOTION Sir Isaac Newton proposed

some statements to explain the way things move Anything that is not moving will stay that way unless a force makes it move Anything that is moving will keep moving at the same speed and in the same direction unless a force makes

it change THE EFFECT OF MASS The more massive something is, the greater its inertia This means it takes a greater force to change its motion Eg: it takes a smaller force to stop a pebble roll down a hill than to stop a massive rock

TYPES OF FORCES Contact Friction NonContact Contact forces touch

an object Gravity Pull Magnetic Push

Electrost atic Non-contact forces act at a distance