Y7 – TERM 2 REVISION Draw the magnetic field around the bar magnet: Why do cars have a maximum speed? As cars get faster, the air resistance acting on them increases. This means that eventually the engine can‘t produce enough force to overcome the air resistance and the car can no longer speed up. What are the advantages of using electromagnets compared to regular magnets? Electromagnets can be turned on and off. They also are much stronger for their size compared to regular magnets. What is drag? Drag is the overall resistive force acting on an object. It includes friction and air resistance. It always acts against the direction of motion. Give three ways in which you can increase the strength of an electromagnet: - add more coils - increase the current/voltage - add an iron core List 3 magnetic materials: - iron - nickel - cobalt List 3 non-magnetic metals: - aluminium - gold - copper What is a resultant force? + A resultant force is the overall force acting on an object when you add the individual forces together. - + - List some uses of electromagnets: used in scrap yards to pick up metal electric bells guitar pick-ups doorbells How can forces affect motion? - make things start moving - make things stop moving - speed things up - slow things down - change direction of an object - change the shape of an object Explain the difference between hard and soft magnets and give an example of each: Hard magnetic materials such as steel are difficult to magnetise but stay magnetic for a long time. Soft magnetic materials such as iron are easy to magnetise but lose their mangetism easily. Explain what is meant by terminal velocity: Terminal velocity is when the forces acting of a falling object are balanced. This means that the air resistance is equal to the weight of the object so it can not speed up any further. Terminal velocity can be decreased by increasing the surface area of the object. What is acceleration? Acceleration is the rate of change of velocity. This is how quickly an object speeds up, slows down or changes direction. It‘s unit is a metre per second squared which can be written as m/s/s; m/s2; m s-2 . Write down the equation, with units which links weight, mass and gravity: Weight = mass x gravity (N) (kg) (N/kg)

For each scenario on this page, write what size and direction of each resultant force is and then describe the motion of the object. 5 N 100 N 2 N 4 N 6 N 5 N 500 N 2 N Size of Resultant Force: 0 N Direction: None Motion: Stationary (with only upwards and downwards forces present we can assume the downwards force is weight and upwards is the reaction force) Size of Resultant Force: 2 N Direction: To the right Motion: Accelerating to the right (Speeding up) Size of Resultant Force: 400 N Direction: Downwards Motion: Accelerating downwards (Speeding up – he is falling through the air) 1 N 4 N 70 N 5 N 5 N 6 N 3 N 50 N 50 N 1 N 4 N 40 N Size of Resultant Force: 3 N Direction: To the left Motion: Accelerating to the left (Speeding up) Size of Resultant Force: 0 N Direction: None Motion: Moving with constant speed. (The presence of the arrows to the left and right show that he must be moving but as the force are balanced, his speed is constant) Size of Resultant Force: 30 N Direction: Upwards Motion: Accelerating upwards. (Speeding up – he is jumping upwards)