Forces and Movement

Average Speed

When an object moves in a straight line at a steady speed, you can calculate its avearge speed if you know how far it travels. The equation for this is: 

Average Speed is measured in metres per second, M 

Distance Moved is measured in Metres, M

Time Taken is meausred in Metres Per Second, S

Example 1

A car travels 300m in 20s, the average speed for the car is 

300/20= 15 m/s 

Distance Time Graphs

A distance-time graph shows how far something travels over a period of time. The vertical axis of a distance-time graph is the distance travelled from the start. The horizontal axis is the time from the start.

Features of the Graphs 

When an object is stationary, the line on the graph is horizontal. When an object is moving at a steady speed in a straight line, the line on the graph is straight but sloped. 

Acceleration : You can calculate the acceleration of an object from its change in velocity and the time taken. Velocity is not exactly the same as speed. Velocity has a direction as well as a speed. For example, 15 m/s is a speed, but 15 m/s North is a velocity (North is the direction).

The Equation: When an object moves in a straight line with a constant acceleration, you can calculate its acceleration if you know how much its velocity changes and how long this takes.

The units for acceleration are commonly written as m/s/s or m/s². The equation for acceleration can also be represented as:       For example, a car accelerates in 5 s from 25 m/s to 3 5m/s. Its velocity changes by 35 - 25 = 10 m/s. Therefore its acceleration is 10 ÷ 5 = 2 m/s²

the velocity ofan object is its speed in a particular direction. Two cars travelling at the same speed but in oppisite directions have different velocities. 

A velocity-time graph shows the speed and direction an object travels over a speific period of time. Velocity-time graphs are also called speed-time graphs. 

The vertical axis of a velocity-time graph is the velocity of the object. The horizontal axis is the time from the start. 

Features of the Graphs 

when an object is moving with a constant velocity, the line on the graph is horizontal. When the horizontal line is at zero velocity, the object is at rest. When an object is undergoing constant acceleraion, the line on the graph is straight but sloped.

Types Of Forces

A force is any influence that causes an object to undergo a specific change. Related concepts include:

• thrust-increases the velocity of an object 
• air resistance- decreases the velocity of an object 
• torque- changes the rotation of an object 

In Newtons laws of motion, Isaac Newton made statements about the effect of balanced and unbalanced forces. 

Newton's First Law of Motion states that objects with balanced forces acting on them will stay at rest or stay in constant motion. 

Newton Discovered that objects will continue to do what they are doing utnil an unbalanced force acts on the object. From this we can determine that: 

• Forces act on on objects 
• Forces cause changes 

We can also determine that forces acting on an object can change the shape of the object, and the direction in which the object is moving. 

Newtons Second Law of Motion states that when an unbalanced force acts on an object: 

• The direction of the objects acceleration is the same as the direction of the unbalanced force
• The magnitude of the object's acceleration varies in direct proportion with the size of an unbalanced force
• the magnitude of the object's acceleration vaires inversely with the mass of the object