1. Forces

2. What is a Force?
A force is a push or a pull on an object.

3. Push-me pull-you?

4. The Effects of a Force A force can: Change the shape of an object
Change the speed of an object

5. The Effects of a Force
A force can:
Change the direction of an object

6. Contact Forces These need to touch an object to produce an effect
E.g. kicking a ball, striking a match and friction.

7. Non-Contact Forces
These can exert an effect on an object without being in contact with the object.
E.g. a magnet attracting a paperclip, gravity and an electrostatic force.

8. Mass and Weight All objects have mass.
This is the amount of matter in an object, it stays constant no matter where the object is.
Mass is measured in g and kg.
Weight is actually a force.
Weight is caused by the force of gravity pulling down on an object.
Weight is measured in Newtons (N)
Weight varies with location.

9. Measuring Forces The symbol for force is F
The units for force are Newtons (N).
A force of 1N is defined as the force needed to make a 1kg mass accelerate across a flat, frictionless surface at 1ms-2
Forces are measured using a Force meter.

10. Drawing Forces Arrows are used to represent forces
The arrowhead shows the direction of the force.
The length of the arrow show the magnitude (size) of the force. 2N 6N
A two Newton upward force
A six Newton force to the right

11. Balanced and Unbalanced Forces
When the forces on an object are equal they are called balance forces
The object will be either stationary or at constant speed
When the forces on an object are not equal they are called unbalanced forces
The object will be changing speed (speeding up or slowing down)

12. Balanced and Unbalanced Forces
The net force is the difference between the largest and the smallest force and is in the direction of the largest force

13. Forces on an Object Support Force Thrust Force Drag Force
Gravity Force
All objects have a number of forces acting on them at any one time. The relative size and direction of the forces determine the motion of the object according to Newton’s first law
Balanced forces – object stationary or at constant speed
Unbalanced forces –object accelerating in the direction of the largest force.

14. Newtons’ Laws of Motion
Isaac Newton in 1729 came up with three laws of motion:
If the forces on an object are balanced the object will be either stationary or at constant velocity
An unbalanced net force will cause an object to accelerate in the same direction as the force and at a rate that is inversely proportional to the mass of the object (F=ma)
All forces occur in pairs, and these two forces are equal in magnitude and opposite in direction

15. Newtons’ Laws of Motion
If the forces on an object are balanced the object will be either stationary or at constant velocity

16. Newtons’ Laws of Motion
An unbalanced net force will cause an object to accelerate in the same direction as the force and at a rate that is inversely proportional to the mass of the object (F=ma)

17. The Equation
F = ma
Is saying…the amount of force needed to change the speed of an object will depend on:
How much mass the object has (m)
How fast you want to change the speed (a)

18. Newtons’ Laws of Motion
All forces occur in pairs, and these two forces are equal in magnitude and opposite in direction

19. Equal and Opposite Forces
Forces act in pairs, these pairs are equal in size and opposite in direction
Not always easy to see their effects
Think skating
What about giving someone a shove on the ice?