Physics 4

Physics 4

1. Describing Motion

   • The speed of a moving object can be calculated if the distance travelled and the time taken are known. The faster an object moves, the steeper is the line representing it on a distance-time graph
   • Speed is distance divided by time taken.
     • Speed (meters per second) = Distance travelled/Time taken
   • When an object moves in a straight line at a steady speed, you can calculate its average speed if you know how far it travels and how long it takes. This equation shows the relationship between speed, distance travelled and time taken

2. Distance Time Graphs

   • The vertical axis of a distance-time graph is the distance travelled from the start, and the horizontal axis is the time taken from the start
   • When an object is stationary, the line on the graph is horizontal. When an object is moving at a steady speed, the line on the graph is straight, but sloped
     • Note that the steeper the line, the greater the speed of the object

3. Time Graphs

4. Velocity Time Graphs

   • 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. One velocity will be positive, and the velocity in the other direction will be negative.
   • The vertical axis of a velocity-time graph is the velocity of the object and the horizontal axis is the time taken from the start
   • When an object is moving with a constant velocity, the line on the graph is horizontal. When an object is moving with a steadily increasing velocity, or a steadily decreasing velocity, the line on the graph is straight, but sloped. The diagram shows some typical lines on a velocity-time graph

5. Forces

   • 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
   • Zero resultant force: When all the forces are balanced, the resultant force is zero. In this case: A stationary object remains stationary A moving object keeps on moving at the same speed and in the same direction
   • When all the forces are not balanced, the resultant force is not zero. In this case, an object accelerates in the direction of the resultant force. This means that: 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
   • An object will accelerate in the direction of the resultant force. The bigger the force, the greater the acceleration. Doubling the size of the (resultant) force doubles the acceleration
   • An object will accelerate in the direction of the resultant force. A force on a large mass will accelerate it less than the same force on a smaller mass. Doubling the mass halves the acceleration
   • How to calculate Acceleration
     • Acelleration = Force/Mass
       • E.G: 50 ÷ 10 = 5 m/s2

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