Forces and Motion (Section 1)

Forces and Motion - a) Units

1.1 use the following units: kilogram (kg), metre (m), metre/second (m/s), metre/second2 (m/s2), newton (N), second (s), newton per kilogram (N/kg), kilogram metre/second (kg m/s).

kilogram (kg) = metric way of measuring mass.

metre (m) = metric measure for distance. 

metre/second (m/s) = this measures speed. (speed = distance/time)

metre/second^2 (m/s^2) = measure of acceleration.

newton (n) = measure of force. 

second (s) = measure of time. 

newton per kilogram (N/kg) = measure of acceleration. 

kilogram metre/second (kg m/ s) = measure of momentum. 

b) Movement and position

1.2 plot and interpret distance-time graphs 

Distance time graphs show the relationship between the distance travelled and the time taken to travel this distance. 

Plotting distance-time graphs

The y-axis refers to the distance travelled along the journey, and the x-axis refers to the time taken to travel this distance.  To plot, mark the distance travelled at each point and correspond with the time taken to get there. Continue horizontally along the line of your last point to represent a stop in the journey, while displaying the time that passed during this pause. 

Interpreting distance-time graphs 

• As mentioned before, the y-axis of a distance-time graph will refer to the distance travelled, and the x-axis will refer to the time taken to travel this distance. 
• Therefore, gradient of the line (change in y/change in x) will equal the speed of the journey (speed = distance/time).
• A straight horizontal line represents a stop in the journey, with the time obviously continuing but not the distance.
•  An upward line shows a journey away from the starting point, while a downward line shows a journey back to the starting point. 
• The steeper the line, the faster the object is travelling. 

1.3 know and use the relationship between average speed, distance moved and 

time: 

 average speed = distance moved/time taken. 

1.4 describe experiments to investigate the motion of everyday objects such as

toy cars or tennis balls

You can use the triangle above for this. Remembering that speed = distance/time, you can find the motion of an everyday object. For example, if an object travels 5m in 10seconds then motion(speed) = distance/time = 5/10 = 0.5m/s, 

1.5 know and use the relationship between acceleration, velocity and time:

Acceleration = change in velocity/time taken 

so, a = (v-u)/t 

where v = final velocity, 

          u = initial velocity 

          t = time 

1.6 plot and interpret velocity-time graphs

• Gradient = acceleration
• Flat sections represent steady speed. 
• The steeper the graph, the greater the acceleration or deceleration. 
• Uphill sections (/) = acceleration
• Downhill sections = deceleration.
• A curve represents a changing acceleration. 
• The area under any section of the graph = the distance travelled in that time interval. 
• Speed at any point = read off value from the velocity axis. 

1.7 determine acceleration from the gradient of a velocity-time graph

The acceleration of a velocity-time graph = the gradient. 

Gradient = vertical/horizontal 

              = velocity/time 

In the velocity-time graph displayed above, the gradient of the first line = velocity/time 

 = 20/20 

= 1m/s^2                    

     

1.8 determine the distance travelled from the area between a velocity-time

graph and the time axis.

The distance can be calculated by finding the area between the velocity axis and the time axis.

So, the area of triangle= 1/2 x 8 x 4 

                                     = 16

Area of rectangle = 8 x 6 

                             = 48

Total area = 16 + 48 

                  = 64m.