WA2

• Frictional force is the force that opposes the motion between two surfaces in contact. It is the force that allows us to hold our pen
• Elastic force is the force acting on a stretched or compressed elastic object to return it to its original shape and size
• Gravitational force is the force between two objects. When a planet exerts gravitational force on an object and pulls it towards the center, the object has weight.
• Due to its massive, the moon can exert a gravitation force that is large enough to affect the seawater levels on Earth. The gravitational force on the water changes as Earth rotates. The water that is facing the moon will experience a larger gravitational force, resulting in a high tide
• When unlike poles are brought close to each other, they pull together due to the magnetic force of attraction. When the like poles are brought close to each other , they push apart due to the magnetic force of repulsion
• The Maglev train works on the principle of magnetic repulsion between the train and the track. Maglev train floats on air due to the magnetic repulsion of like poles. This greatly reduce the friction between the tracks and train, allowing the train to travel at a higher speed.
• Effects of Force: - A force can change a moving object's direction -A force can cause a turning effect in an object - A force can change the pressure of an object -A force can change the shape and size of an object - A force can make a stationary object move - A force can change the speed of a moving object - A force can stop a moving object
• A force applied on an object can cause a turning effect about a fixed point called the pivot which helps us to carry out an action with little force
• The mass of an object stay constant and can never change
• Mass is the amount of matter in an object. The SI unit of Mass is Kilogram (KG). Mass can be measured using a electronic balance
• Weight is the measure of gravitational force acting on an object. The SI unit for weight is Newton (N). Weight can be measured using a spring balance. The spring in a spring balance stretches when a force pulls on it. As weight is a force, the weight of an object can be read off directly from the scale of the spring balance
• The mass of an object does not change regardless of location
• The weight of an object depends on the gravitational force exerted on the object, which may change with location
• The smaller the contact area, the larger the pressure is exerted
• The larger the contact area, the smaller the pressure exerted
• The pressure exerted on an object is affected by the amount of force applied to the contact area of the object. A smaller force applied to a contact area of an object will exert a smaller pressure. Conversely, a larger force applied to a contact area of an object will exert a larger pressure
• The larger the weight, the larger the force applied. Hence the pressure exerted on an object is larger, when the contact area remains constant
• Pressure = Force/Area. Pressure is force per unit area.
• Block A exerts a larger pressure on the table as the contact area of Block A is smaller than that of Block B. As pressure = Force/area, for the same amount of force (Weight) applied, the pressure exerted by block A will be larger than Block B since both blocks have the same total weight
• Block A exerts a pressure that is three times Block B as the contact area of Block A is one-third of Block B. As pressure = force/area, for the same amount of force (weight) applied, the pressure exerted by Block A will be three times that of Block B.
• Liquid pressure at a point within the liquid depends on the depth of the point. As there are more water particles at the bottom of the container, the gravitational force on water particles pushing down on the bottom of the pool applies a larger force. Hence there is a higher pressure exerted at the bottom of the pool
• The pressure deep below water can be very high, a strong body is needed to withstand high pressure. Every submarine has a depth limit to ensure that the submarine is at a safe depth so that the water pressure is not high enough to damage the submarine physical strucutre
• The pressure acting on the body increases as he moves closer to the bottom of the pool. This is due to the increased weight of the column of water above him.
• The Earth is surrounded by a thick layer of air and air particles are light, occupy spaces, and have mass, the layer of air particles pushes down on Earth's surface due to Earth's Gravitational force, exerting a pressure of about 100000 Pa at sea level. The layer of air also exerts pressure on us and all objects on Earth. When we are at a height above sea level, fewer air particles push down on us. Hence, the atmospheric pressure exerted on us decrease
• Examples: Drinking Straw- When someone sucks on a straw, some air is removed from the straw. The air pressure in the straw decreases and become lower than the surrounding atmospheric pressure. The water then rises up the straw
• Suction cup hook- When we press a suction cup hook against a smooth surface, the air is pushed out from under the suction cup. The air pressure between the suction cup and the smooth surface decreases. It becomes lower than the atmospheric pressure. The higher atmospheric pressure holds the suction cup hook in one place on the surface
• Energy refers to the capacity to do work. The SI unit for Energy is Joules. Energy can change the state of matter. Energy can be transferred from one place to another.
• The conservation of energy is a scientific principle that states that the total amount of energy in an isolated system remains constant as energy cannot be created or destroyed but can only be converted from one form to another.
• Kinetic energy: Is the energy that moving items have.
• Electrical energy: can be used to power electrical appliances like the television and electric fan.
• Sound energy: enable us to listen to our favourite music
• Light energy: allows us to see thing
• Heat energy: enable us to heat our food
• Chemical Potential energy: in batteries can be used as an energy source when converted to electrical energy.
• Gravitational potential energy: which an object possesses due to its position can cause an object to move faster when converted to kinetic energy.
• When an object moves in the same direction as the force applied on it, there is work done and it involves a transfer of energy
• Work is not done by (subject) on an object when it did not move a distance in the same direction as the direction of the force applied on the object
• Energy is transferred when a force applied to an object causes it to move a distance in the same direction as the force
• Energy is transferred from (subject) to the object when the object moves a distance in the same direction as the force exerted by the (subject) on the object.
• No work is done by the (subject) to keep the object in a stationary position as it does not cause the object to move a distance in the same direction as the force applied to it