Forces

Forces

Forces4th July 2015What is a Force?A force can be a push or pull.

A force has magnitude and direction.

A force can arise when one object exerts a force onto another object.

A force does not necessarily result in motion.A force...... is a push or pull.... acts on an object.... requires an agent.... is a vector.... is a contact force or a long-range force.

3Forces can effect things in 3 ways. Can you name them? 7K Identifying forces Effects of a force Effect 3. A force can change the direction of an object.

Effect 2. A force can change the speed of an object, making it faster or slower.

Effect 1. A force can change the shape of an object.

How is Force Measured?SI unit for Force is Newtons (N).

The more Newtons, the greater the force.

Hence the value of the newtons of a given force is the magnitude. How is Force Measured It is measured using the spring scale.

It consists of aspring fixed at one end with a hook to attach an object at the other. It works byHookes Law, which states that the force needed to extend a spring is proportional to the distance that spring is extended from its rest position.How is Force Measured A spring balance (spring scale) can only measure weight and not mass.

SI unit of weight is Newtons (N).

Gravity or also known as a downward force is used to operate the spring scale.

Example of A Spring Scale

NewtonsGramsThe mass of an object can be measured in terms of newtons (N). This is used by Karung guni men to weigh a bundle of newspapers and quote a price when old newspapers are sold to them Gravity A downward force and also a non-contact force The pulling force of gravity always acts towards the centre of the Earth, wherever you are on the planet.

Anon-contact forceis aforceapplied to an object by another body that is not in direct contact with it. The most familiar example of a non-contact force isweight. Uses of Gravity A downward Force Why does rain always fall downwards towards the Earth?

Why dont people on the other side of the Earth fall off into outer space?

Why doesnt water come out ofthe tap sideways?

Weight The effect of the force of gravity on an object is called the objects

weight Weight is a force and is measured in Newtons.

How is weight different to mass? Does Gravity differ based on your location?Gravity changes depending on where you are in the Universe. So the answer is YES!

What happens to weight and mass when gravity changes?

Location: Planet Earth!

Location: The Moon!

Location: Outer Space!!

Other types of non-contact forceMagnetic force when two magnets of unlike poles attract each other.

Magnetic force when two magnets of like poles repel each other.

Electrical force Non-contact force of electrical charges. (Remember your circuit topic?)

Contact forces- Involve physical contact between objects.Contact ForceContact forces arise when two objects interact due to surfaces in contact. These forces can be broken into two components parallel and perpendicular to the surface

The component parallel to the surface is the friction force.

The component perpendicular to the surface is the normal force. (normal is a mathematical term meaning perpendicular.)19Be prepared to make reasonable estimations and state your assumptions when solving problems. Be aware of significant digits in your answers. (Keep lots of digits until the final calculation, then round to the appropriate precision. For intermediate steps, remember to keep one extra significant digit3, 2, 1 Contact!What are some contact forces?A contact force is a push or a pull on one object by another object that is touching it.

An applied force is a type of contact force in which one object directly pushes or pulls on another object. For example, in tug of war, you apply a pulling force to the rope.

A spring force (or elastic force) is the force exerted by a bending or stretching object on any object that is attached to it.

2020What are some examples of contact forces?Friction is the force an object exerts on an object that moves across it. The force of friction tends to oppose the motion of the object.

Air resistance is a type of contact force that air exerts on moving objects. Like friction, air resistance tends to oppose the motion of an object. When an object is thrown downwards, gravity pulls it downs, hence air resistance would act upwards.

2121

7K Friction What is friction? Friction occurs when any two surfaces move against each other and tries to stop the movement. Heat is generated as a result of friction.

Which type of surface generates more friction,a rough surface or a smooth surface?

Put your palms together and rub hard. What happens?

frictionYou are creating the force called

.A foot kicking a soccer ballAn apple falling off a treeA paper clip sliding towards a magnetA bat striking a baseballTwo magnets pushing apart from one anotherThe moon orbiting the EarthA compass needle turning NorthA hand pushing an objectShoes rubbing against the floor

Classify the ForcesHave students specify contact or non- contact as well as specific type of force. For example: A foot kicking a soccer ball is a contact force: applied force.24Homework 1. The units that forces are measured in are calleda) Joules.b) kilograms.c) Newtons.2. Gravity and magnetism are examples ofa) contact forces.b) non-contact forces.c) police forces.Homework3. The force that occurs when two surfaces move against each other is calleda) contact force.b) fiction.c) friction.4. In icy weather roads are covered with sand. How does the sand effect the amount of friction between car tyres and the road? a) Reduces friction.b) Increases friction.c) Has no effect.Homework5. A dog being taken for a walk is pulling on the lead held by its owner. The pulling force of the dog increases. What happens to the speed of its owner?a) Speeds up.b) Slows down.c) Changes direction.6. The upwards force that slows down a sky diver as they fall through the air is calleda) weight.b) air conditioning.c) air resistance.Homework7. The pulling force of the Earths gravity always acts towards the centre ofa) the Moon.b) the Earth.c) the Sun.8. A computer on a desk does not move because there area) no forces acting on it.b) unbalanced forces acting on it.c) balanced forces acting on it.Homework9. An astronaut drops a 1 kg bar of chocolate in outer space. What is the weight of the bar of chocolate?a) 10 N.b) 1 N.c) 0 N.10.A spacecraft has a mass of 9000 kg on Earth. What would its weight be on the Moon?a) 1500 N.b) 9000 N.c) 54 000 N.E-Learning Homework Download the powerpoint slides from google drive and go through the animation.

Press F5 to activate slides and follow instructions.

Click on the picture to find the force

Homework Download the powerpoint slides from google drive and go through the animation.

Press F5 to activate slides and follow instructions. What is Friction?Click on blue arrow in a circle to watch animation