Momentum- You can calulate the momentum of an object with formula:
(kilogram metre/ second, kg m/s= (kilograms, kg x (metres/ second, m/s)
Momentum has both mass and velocity. A force acting on a body that is moving or is able to move. It changes momentum
Resultant force= mass x acceleration (newtons x kilograms x metres/ second
The resultant force: An object may have several different forces acting on it, which can have different strengths and directions. But they can be added together to give the resultant force. This is a single force that has the same effect on the object as all the individual forces acting together.
When all the forces are balanced, the resultant force is zero. In this case: a stationalry object remains stationary, a moving object keeps on moving at the same speed in the same direction.
When all the forces are not balanced, the resultant force is not zero. In this case:
- A stationary object begins to move in the direction of the resultant force.
- A moving object speeds up, slows down or changes direction depending on the direction of the resultant force.
Velocity and acceleration
Velocity is the speed in a given direction. Acceleration is change of velocity per second. A body travelling at a steady speedis accelerating if its direction is changing.
Acceleration: Change in velocity (metre/ sec, m/s) divided by time taken
- For example, a car accelerates in 5s from 25m/s to 35m/s.
- Its velocity changes by 35 - 25 = 10m/s.
- So its acceleration is 10 ÷ 5 = 2m/s2.
The velocity of an object is its speed in a particular direction. This means that two cars travelling at the same speed, but in opposite directions, have different velocities.
The vertical axis of a velocity-time graph is the velocity of the object. The horizontal axis is the time from the start.
Insulating materials: Metals are good conductors, which means that electrical charges move easily through them. Materials such as plastic, wood, glass and polythene are insulators. This means they do not allow electrical charges to move through them. Some insulators can be electrically charged when they are rubbed together.
How can you tell if an insulator is charged?
- If a plastic rod is rubbed with a duster it attracts small pieces of paper.
- When a balloon is rubbed on a jumper it can stick to a wall.
Some dusters are designed to become charged so that they attract dust.
Resistance is measured in ohm's. The symbol for ohm's looks like this Ω. The greater the ohm's the greater the resistance. The eqation below shows the relationship between voltage, current and resistance:
potential difference (volt, V) = current (ampere, A) × resistance (ohm, Ω )
The current flowing through a resistor at a constant temperature is directly proportional to the voltage across the resistor. So, if you double the voltage, the current also doubles. This is called Ohm's Law.